.github: clean up unused containers and images before starting

Error: error creating container storage: the container name "infamy0" is already in use by "2011c2d7cb1737b788b854a8bd08e519f3cbd6e36dae4975784978cff1f238fc". You have to remove that container to be able to reuse that name.: that name is already in use
make[1]: *** [/home/github-runner/actions-runner/_work/infix/infix/test/test.mk:6: test-unit] Error 125

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

.github/workflows/regression.yml

@@ -22,6 +22,9 @@ jobs:
       - uses: actions/checkout@v4
         with:
           submodules: 'true'
+      - name: Clean up cruft ...
+        run: |
+          ./test/env -c
       - name: Set Build Variables
         id: vars
         run: |