fix[ci]: pin nightly for miri (#6448)

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---------

Signed-off-by: Joe Isaacs <joe.isaacs@live.co.uk>

Author: joseph-isaacs

.github/workflows/ci.yml

@@ -23,6 +23,7 @@ permissions:
 env:
   CARGO_TERM_COLOR: auto
   RUST_BACKTRACE: 1
+  NIGHTLY_TOOLCHAIN: nightly-2026-02-05
 
 jobs:
   lint-toml:
@@ -283,10 +284,10 @@ jobs:
       - id: setup-rust
         uses: ./.github/actions/setup-rust
         with:
-          toolchain: nightly
+          toolchain: ${{ env.NIGHTLY_TOOLCHAIN }}
           repo-token: ${{ secrets.GITHUB_TOKEN }}
       - name: Rust Lint - Format
-        run: cargo +nightly fmt --all --check
+        run: cargo +$NIGHTLY_TOOLCHAIN fmt --all --check
       - name: Rustc check
         run: RUSTFLAGS="-D warnings" cargo check --locked --all-features --all-targets
       - name: Rustc check (release)
@@ -404,7 +405,7 @@ jobs:
         env:
           RUSTFLAGS: "-Cinstrument-coverage -A warnings --cfg vortex_nightly"
         run: |
-          cargo +nightly nextest run --locked --workspace --all-features --no-fail-fast
+          cargo +$NIGHTLY_TOOLCHAIN nextest run --locked --workspace --all-features --no-fail-fast
       - name: Install llvm-tools-preview
         run: rustup component add llvm-tools-preview
       - name: Generate coverage report
@@ -463,7 +464,7 @@ jobs:
         uses: ./.github/actions/setup-rust
         with:
           repo-token: ${{ secrets.GITHUB_TOKEN }}
-          toolchain: nightly
+          toolchain: ${{ env.NIGHTLY_TOOLCHAIN }}
           components: "rust-src, rustfmt, clippy, llvm-tools-preview"
       - name: Install build dependencies
         run: |
@@ -478,11 +479,11 @@ jobs:
           RUSTFLAGS: "-A warnings -Zsanitizer=address -Zsanitizer=leak --cfg disable_loom --cfg vortex_nightly -C debuginfo=2 -C opt-level=0 -C strip=none"
         run: |
           # Build with full debug info first (helps with caching)
-          cargo +nightly build --locked --all-features  \
+          cargo +$NIGHTLY_TOOLCHAIN build --locked --all-features  \
             --target x86_64-unknown-linux-gnu \
             -p vortex-buffer -p vortex-ffi -p vortex-fastlanes -p vortex-fsst -p vortex-alp -p vortex-array
           # Run tests with sanitizers and debug output
-          cargo +nightly nextest run \
+          cargo +$NIGHTLY_TOOLCHAIN nextest run \
             --locked \
             --all-features \
             --no-fail-fast \
@@ -516,7 +517,7 @@ jobs:
       - uses: ./.github/actions/setup-rust
         with:
           repo-token: ${{ secrets.GITHUB_TOKEN }}
-          toolchain: nightly
+          toolchain: ${{ env.NIGHTLY_TOOLCHAIN }}
           components: "rust-src, rustfmt, clippy, llvm-tools-preview"
       - name: Install nextest
         uses: taiki-e/install-action@v2
@@ -528,9 +529,9 @@ jobs:
           FLAT_LAYOUT_INLINE_ARRAY_NODE: true
         run: |
           # Build with full debug info first (helps with caching)
-          cargo +nightly build --locked -p vortex-cuda -p vortex-file -p vortex-test-e2e-cuda --all-features --target x86_64-unknown-linux-gnu
+          cargo +$NIGHTLY_TOOLCHAIN build --locked -p vortex-cuda -p vortex-file -p vortex-test-e2e-cuda --all-features --target x86_64-unknown-linux-gnu
           # Run tests with sanitizers and debug output
-          cargo +nightly nextest run \
+          cargo +$NIGHTLY_TOOLCHAIN nextest run \
             --locked \
             -p vortex-file \
             -p vortex-cuda \
@@ -557,7 +558,7 @@ jobs:
           CARGO_TARGET_X86_64_UNKNOWN_LINUX_GNU_RUNNER: compute-sanitizer --tool initcheck --error-exitcode 1
         run: cargo test -p vortex-cuda
       - name: Build cudf test library
-        run: cargo +nightly build --locked -p vortex-test-e2e-cuda --target x86_64-unknown-linux-gnu
+        run: cargo +$NIGHTLY_TOOLCHAIN build --locked -p vortex-test-e2e-cuda --target x86_64-unknown-linux-gnu
       - name: Download and run cudf-test-harness
         run: |
           curl -fsSL https://github.com/vortex-data/cudf-test-harness/releases/latest/download/cudf-test-harness-x86_64.tar.gz | tar -xz
@@ -790,13 +791,13 @@ jobs:
       - uses: ./.github/actions/setup-rust
         with:
           repo-token: ${{ secrets.GITHUB_TOKEN }}
-          toolchain: nightly
+          toolchain: ${{ env.NIGHTLY_TOOLCHAIN }}
           components: "rust-src, rustfmt, clippy, miri"
       - uses: taiki-e/install-action@v2
         with:
           tool: nextest
       - name: Run Miri
-        run: cargo +nightly miri nextest run --no-fail-fast -p vortex-buffer -p vortex-ffi
+        run: cargo +$NIGHTLY_TOOLCHAIN miri nextest run --no-fail-fast -p vortex-buffer -p vortex-ffi
 
   generated-files:
     name: "Check generated source files are up to date"
@@ -807,15 +808,15 @@ jobs:
       - uses: ./.github/actions/setup-rust
         with:
           repo-token: ${{ secrets.GITHUB_TOKEN }}
-          toolchain: nightly
+          toolchain: ${{ env.NIGHTLY_TOOLCHAIN }}
       - uses: ./.github/actions/setup-flatc
       - name: "regenerate all .fbs/.proto Rust code"
         run: |
           cargo xtask generate-fbs
           cargo xtask generate-proto
       - name: "regenerate FFI header file"
         run: |
-          cargo +nightly build -p vortex-ffi
+          cargo +$NIGHTLY_TOOLCHAIN build -p vortex-ffi
       - name: "Make sure no files changed after regenerating"
         run: |
           git status --porcelain