Install python on $PATH and check version

Author: dandavison

.github/workflows/ci.yml

@@ -27,8 +27,22 @@ jobs:
       - uses: actions/checkout@v4
         with:
           submodules: recursive
+      - run: uv --preview python install --default ${{ matrix.python }}
       - run: uv tool install poethepoet
       - run: uv sync --group=dsl --group=encryption --group=trio-async --python ${{ matrix.python }}
+      - name: Check python version
+        shell: bash
+        run: |
+          actual=$(uv run python -c "import sys; print('.'.join(map(str, sys.version_info[:2])))")
+          if [[ "$actual" != "${{ matrix.python }}" ]]; then
+            echo "Python version in use by uv ($actual) does not match intended version (${{ matrix.python }})"
+            exit 1
+          fi
+          actual=$(python -c "import sys; print('.'.join(map(str, sys.version_info[:2])))")
+          if [[ "$actual" != "${{ matrix.python }}" ]]; then
+            echo "Python version on $PATH ($actual) does not match intended version (${{ matrix.python }})"
+            exit 1
+          fi
       - run: poe lint
       - run: mkdir junit-xml
       - run: poe test -s --junit-xml=junit-xml/${{ matrix.python }}--${{ matrix.os }}.xml