[pypi] change python version to supported and add ruff linter

.github/workflows/lint.yml

@@ -0,0 +1,11 @@
+name: Lint and check
+on: [ push, pull_request ]
+jobs:
+  ruff:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-python@v5
+        with:
+          python-version: "3.12"
+      - uses: chartboost/ruff-action@v1

.github/workflows/release.yml

@@ -17,15 +17,15 @@ jobs:
       - name: "Checkout code"
         uses: actions/checkout@v4
 
-      - name: Set up Python 3.12
-        uses: actions/setup-python@v4
+      - name: Set up Python 3.9
+        uses: actions/setup-python@v5
         with:
-          python-version: "3.12"
+          python-version: "3.9"
 
       - name: Setup pdm
         uses: pdm-project/setup-pdm@v3
         with:
-          python-version: "3.12"
+          python-version: "3.9"
 
       - name: Build package
         run: pdm build

pyproject.toml

@@ -13,7 +13,7 @@ maintainers = [
 description = "Stacked PRs for GitHub."
 readme = "README.md"
 license = { file = "LICENSE" }
-requires-python = ">=3.8"
+requires-python = ">=3.9"
 keywords = ["stacked-prs", "github", "pull-requests", "stack-pr", "git", "version-control"]
 classifiers = [
     "Development Status :: 5 - Production/Stable",