workflows: Skip system tests for ceph and lvm on push and schedule.

Signed-off-by: Mark Laing <mark.laing@canonical.com>

.github/workflows/tests.yml

@@ -394,6 +394,7 @@ jobs:
         if: env.GOCOVERDIR != ''
 
       - name: "Run system tests (${{ matrix.go }}, ${{ matrix.suite }}, ${{ matrix.backend }})"
+        if: (github.event.name != 'pull_request' && github.event.name != 'schedule') || (matrix.backend != 'ceph' && matrix.backend != 'lvm')
         run: |
           set -eux
           chmod +x ~