CI: Don't fail fast on container image build job failure

Previously if one of the container image build jobs (CS8, Ubuntu)
failed, the other would be cancelled. This is not necessarily helpful,
since the other job may complete successfully.

This change disables this fail fast behaviour.

Author: markgoddard

.github/workflows/stackhpc-container-image-build.yml

@@ -91,6 +91,7 @@ jobs:
     runs-on: [self-hosted, stackhpc-kayobe-config-kolla-builder]
     permissions: {}
     strategy:
+      fail-fast: false
       matrix: ${{ fromJson(needs.generate-tag.outputs.matrix) }}
     needs:
       - generate-tag