move to using setup-action

.github/workflows/tests.yml

@@ -25,7 +25,6 @@ jobs:
 
   test-job:
     strategy:
-      fail-fast: false
       matrix:
         os: [ubuntu-20.04, ubuntu-22.04, windows-2019, macos-13]
         # Python 3.8 is what we currently support for running cohortextractor
@@ -42,14 +41,11 @@ jobs:
         with:
           persist-credentials: false
 
-      - name: Set up Python ${{ matrix.python }}
-        uses: actions/setup-python@v5
+      - uses: "opensafely-core/setup-action@v1"
         with:
           python-version: ${{ matrix.python }}
-          cache: "pip"
           cache-dependency-path: requirements.*.txt
-
-      - uses: extractions/setup-just@69d82fb0233557aec017ef13706851d0694e0f1d
+          install-just: true
 
       - name: Run actual tests on ${{ matrix.os }}
         if: ${{ matrix.os == 'ubuntu-20.04' || matrix.os == 'ubuntu-22.04' }}