fix: Update Python version support and CI workflow

- Remove Python 3.6, 3.7, 3.8 support (EOL)
- Add Python 3.13 support
- Update CI matrix to test Python 3.9-3.13
- Remove duplicate dependency installation in CI
- Update setup.py classifiers to match supported versions

This reduces CI matrix from 15 jobs to 12 jobs while maintaining
compatibility with current Python versions.

Author: garotm

.github/workflows/workflow.yml

@@ -13,7 +13,7 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest, macos-latest, windows-latest]
-        python-version: ['3.8', '3.9', '3.10', '3.11', '3.12']
+        python-version: ['3.9', '3.10', '3.11', '3.12', '3.13']
 
     steps:
     - uses: actions/checkout@v4
@@ -25,7 +25,6 @@ jobs:
       run: |
         python -m pip install --upgrade pip
         pip install -r requirements.txt
-        pip install black isort flake8 pytest pytest-cov
     - name: Run tests and linting
       run: |
         black --check githubauthlib tests

setup.py

@@ -17,19 +17,18 @@
     url='https://github.com/fleXRPL/githubauthlib',
     license='MIT',
     packages=find_packages(),
-    python_requires='>=3.6',
+    python_requires='>=3.9',
     classifiers=[
         'Development Status :: 4 - Beta',
         'Intended Audience :: Developers',
         'License :: OSI Approved :: MIT License',
         'Operating System :: OS Independent',
         'Programming Language :: Python :: 3',
-        'Programming Language :: Python :: 3.6',
-        'Programming Language :: Python :: 3.7',
-        'Programming Language :: Python :: 3.8',
         'Programming Language :: Python :: 3.9',
         'Programming Language :: Python :: 3.10',
         'Programming Language :: Python :: 3.11',
+        'Programming Language :: Python :: 3.12',
+        'Programming Language :: Python :: 3.13',
         'Topic :: Software Development :: Libraries :: Python Modules',
     ],
 )