Execute delete-pool always if nondocchanges == true (#6626)

## Motivation

The current systest workflow fails when merging a change that doesn't execute system tests, i.e. only documentation was changed. This should fix the issue.

Author: fasmat

.github/workflows/systest.yml

@@ -42,7 +42,7 @@ jobs:
   filter-changes:
     runs-on: ubuntu-22.04
     outputs:
-      nondocchanges: ${{ steps.filter.outputs.nondoc }}
+      nondocchanges: ${{ steps.filter.outputs.nondoc || github.event_name == 'pull_request' }}
     steps:
       - uses: actions/checkout@v4
       - uses: dorny/paths-filter@v3
@@ -172,6 +172,7 @@ jobs:
   systest-gke:
     runs-on: ubuntu-22.04
     if: ${{ needs.filter-changes.outputs.nondocchanges == 'true' }}
+    continue-on-error: true
     needs:
       - filter-changes
       - provision-cluster
@@ -260,7 +261,7 @@ jobs:
 
   delete-pool:
     runs-on: ubuntu-22.04
-    if: always()
+    if: ${{ needs.filter-changes.outputs.nondocchanges == 'true' }}
     needs:
       - filter-changes
       - systest-gke