add apptainer to github actions tests

Author: gilesknap

.github/workflows/_test.yml

@@ -51,7 +51,14 @@ jobs:
           pip-install: ".[dev]"
 
       - name: Run tests
-        run: tox -e tests
+        run: |
+          sudo apt update
+          sudo apt install -y software-properties-common
+          sudo apt install apptainer
+          sudo add-apt-repository -y ppa:apptainer/ppa
+          sudo apt update
+          sudo apt install -y apptainer
+          tox -e tests
 
       - name: Upload coverage to Codecov
         uses: codecov/codecov-action@v4