fix: specify Python 3.9 for Galaxy workflow

- Remove undefined matrix.python-version reference
- Use Python 3.9 to match molecule workflow and requirements

.github/workflows/release-galaxy.yml

@@ -16,10 +16,10 @@ jobs:
       - uses: actions/checkout@v4
         with:
           submodules: recursive
-      - name: Set up Python ${{ matrix.python-version }}
+      - name: Set up Python 3.9
         uses: actions/setup-python@v5
         with:
-          python-version: ${{ matrix.python-version }}
+          python-version: '3.9'
       - uses: actions/cache@v4
         with:
           path: ~/.cache/pip