Drop Python 3.9 support

Author: stefanvanburen

.github/workflows/ci.yaml

@@ -17,7 +17,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python-version: ["3.9", "3.10", "3.11", "3.12", "3.13"]
+        python-version: ["3.10", "3.11", "3.12", "3.13"]
         resolution: ["highest", "lowest-direct"]
     env:
       # Shared env variables for all the tests

pyproject.toml

@@ -9,9 +9,8 @@ readme = "README.md"
 license = "Apache-2.0"
 license-files = ["LICENSE"]
 keywords = ["validate", "protobuf", "protocol buffer"]
-requires-python = ">=3.9"
+requires-python = ">=3.10"
 classifiers = [
-  "Programming Language :: Python :: 3.9",
   "Programming Language :: Python :: 3.10",
   "Programming Language :: Python :: 3.11",
   "Programming Language :: Python :: 3.12",