Update Ruby versions in CI (#64)

* Remove Ruby 2.5, this one is broken outside of the control of the gem
(see #63 (comment))
* Add missing Ruby 4.0

---------

Co-authored-by: Herwin <herwinw@users.noreply.github.com>

Author: herwinw

.github/workflows/test.yml

@@ -17,20 +17,19 @@ jobs:
           - macos
           - windows
         ruby:
-          - "2.5"
           - "2.6"
           - "2.7"
           - "3.0"
           - "3.1"
           - "3.2"
           - "3.3"
           - "3.4"
+          - "4.0"
           - head
         include:
           - { os: windows , ruby: mingw }
           - { os: windows , ruby: mswin }
         exclude:
-          - { os: macos   , ruby: "2.5" }
           - { os: windows , ruby: head }
     steps:
       - uses: actions/checkout@v6