Drop support for Python 3.9

Python 3.9 is officially "end-of-life" since 2025-10-31.

Note: Python 3.14 is officially supported since commit 823a96e "CI: Test
more versions of Python".

Author: adrienverge

.github/workflows/tests.yaml

@@ -42,7 +42,6 @@ jobs:
       fail-fast: false
       matrix:
         python-version:
-          - '3.9'
           - '3.10'
           - '3.11'
           - '3.12'

pyproject.toml

@@ -2,7 +2,7 @@
 name = "yamllint"
 description = "A linter for YAML files."
 readme = {file = "README.rst", content-type = "text/x-rst"}
-requires-python = ">=3.9"
+requires-python = ">=3.10"
 license = "GPL-3.0-or-later"
 authors = [{name = "Adrien Vergé"}]
 keywords = ["yaml", "lint", "linter", "syntax", "checker"]