feat: Enforce Python 3.8+ requirement and add multi-version CI testing

- Add python_requires=">=3.8" to setup.py to enforce minimum version at install time
- Update README to explicitly document Python 3.8+ requirement
- Add CI matrix to test lint/build on Python 3.8-3.14 (7 versions)
- Aligns with actual usage patterns (~99% of downloads on Python 3.8+)
- Prevents future PRs from inadvertently using incompatible syntax

This change protects users by preventing installation on unsupported Python
versions and ensures contributors can see version requirements clearly.

.github/workflows/lint.yml

@@ -15,6 +15,9 @@ jobs:
   lint:
     name: lint
     runs-on: ubuntu-24.04
+    strategy:
+      matrix:
+        python-version: ["3.8", "3.9", "3.10", "3.11", "3.12", "3.13", "3.14"]
 
     steps:
       - name: Checkout repository
@@ -24,7 +27,7 @@ jobs:
       - name: Setup Python
         uses: actions/setup-python@v6
         with:
-          python-version: "3.12"
+          python-version: ${{ matrix.python-version }}
           cache: "pip"
       - run: pip install -r release-requirements.txt && pip install wheel
       - run: flake8 --ignore=E501,E203,W503

README.rst

@@ -9,8 +9,8 @@ The package can be used to backup an *entire* `Github <https://github.com/>`_ or
 Requirements
 ============
 
+- Python 3.8 or higher
 - GIT 1.9+
-- Python
 
 Installation
 ============

setup.py

@@ -50,5 +50,6 @@ setup(
     long_description=open_file("README.rst").read(),
     long_description_content_type="text/x-rst",
     install_requires=open_file("requirements.txt").readlines(),
+    python_requires=">=3.8",
     zip_safe=True,
 )