Add Python version coverage to template CI.

.github/workflows/ci.yml

@@ -6,9 +6,6 @@ on:
       - main
   workflow_call:
 
-env:
-  python_version: "3.9"
-
 defaults:
   run:
     shell: bash # https://github.com/beeware/briefcase/pull/912
@@ -19,6 +16,7 @@ jobs:
     strategy:
       matrix:
         os_name: ["macOS", "windows", "linux"]
+        python-version: ["3.8", "3.9", "3.10", "3.11"]
         framework: ["toga"]
         include:
           - os_name: macOS
@@ -43,7 +41,7 @@ jobs:
       - name: Cache Briefcase tools
         uses: actions/[email protected]
         with:
-          key: briefcase-${{ matrix.platform }}
+          key: briefcase-${{ matrix.platform }}-${{ matrix.python_version }}
           path: |
             ~/.cookiecutters
             ${{ matrix.briefcase-data-dir }}
@@ -55,7 +53,7 @@ jobs:
       - name: Set up Python
         uses: actions/[email protected]
         with:
-          python-version: ${{ env.python_version }}
+          python-version: ${{ matrix.python_version }}
       - name: Install packages
         run: pip install briefcase
       - name: Build Android App