Drop Python 3.7 as a supported Python for textual-dev

We dropped it a wee while back for Textual, let's do that here now too.

Author: davep

.pre-commit-config.yaml

@@ -3,5 +3,5 @@ repos:
     rev: 23.3.0
     hooks:
     - id: black
-      language_version: python3.7
+      language_version: python3.8
 

pyproject.toml

@@ -14,7 +14,6 @@ classifiers = [
     "Operating System :: Microsoft :: Windows :: Windows 11",
     "Operating System :: MacOS",
     "Operating System :: POSIX :: Linux",
-    "Programming Language :: Python :: 3.7",
     "Programming Language :: Python :: 3.8",
     "Programming Language :: Python :: 3.9",
     "Programming Language :: Python :: 3.10",
@@ -27,7 +26,7 @@ include = [
 ]
 
 [tool.poetry.dependencies]
-python = "^3.7"
+python = "^3.8"
 textual = ">=0.36.0"
 aiohttp = ">=3.8.1"
 click = ">=8.1.2"