Remove matrix strategy from GitHub actions

I think the usefulness of this is limited: most tools can probably
migrate from one Python version to another in a single commit, and
replace the Python version in CI at the same time. Let’s simplify the
setup for that common case. (Part of the motivation is that matrix runs
are a bit more annoying to navigate on GitHub, even when there’s only
one instance of them.)

.github/workflows/test.yaml

@@ -5,15 +5,11 @@ on:
 jobs:
   test-defaults:
     runs-on: ubuntu-latest
-    strategy:
-      matrix:
-        python-version:
-          - '3.11'
     steps:
       - uses: actions/checkout@v3
       - uses: actions/setup-python@v4
         with:
-          python-version: ${{ matrix.python-version }}
+          python-version: '3.11'
       - run: pip install --upgrade pip cookiecutter
       - run: |
           cd "${TMPDIR:-/tmp}"
@@ -24,15 +20,11 @@ jobs:
           python example-tool/app.py
   test-all:
     runs-on: ubuntu-latest
-    strategy:
-      matrix:
-        python-version:
-          - '3.11'
     steps:
       - uses: actions/checkout@v3
       - uses: actions/setup-python@v4
         with:
-          python-version: ${{ matrix.python-version }}
+          python-version: '3.11'
       - run: pip install --upgrade pip cookiecutter
       - run: |
           cd "${TMPDIR:-/tmp}"

{{cookiecutter.tool_identifier}}/.github/workflows/test.yaml

@@ -5,15 +5,11 @@ on:
 jobs:
   test:
     runs-on: ubuntu-latest
-    strategy:
-      matrix:
-        python-version:
-          - '3.11'
     steps:
       - uses: actions/checkout@v3
       - uses: actions/setup-python@v4
         with:
-          python-version: {% raw %}${{ matrix.python-version }}{% endraw %}
+          python-version: '3.11'
       - run: pip install --upgrade pip
       - run: pip install -r requirements.txt
       - run: make check