workflows/eval: evaluate all systems to completion on failure

Failing fast hides system-specific evaluation failures, because all of
the currently 4 jobs appear as failed.

.github/workflows/eval.yml

@@ -81,6 +81,7 @@ jobs:
     runs-on: ubuntu-latest
     needs: [ attrs, get-merge-commit ]
     strategy:
+      fail-fast: false
       matrix:
         system: ${{ fromJSON(needs.attrs.outputs.systems) }}
     steps: