fix(ci): only run get-vault-secrets ci from grafana PRs (#472)

The `get-vault-secrets` action only works when run from a `grafana`
repository, so skip this test if the PR is from a different repository. We
will still get a run of this workflow for the change before merging, as we
use merge queues.

Author: iainlane

.github/workflows/test-get-vault-secrets.yaml

@@ -12,6 +12,7 @@ on:
     paths:
       - "actions/get-vault-secrets/**"
       - ".github/workflows/test-get-vault-secrets.yaml"
+
   merge_group:
 
 permissions:
@@ -28,6 +29,12 @@ jobs:
           - invalid
     runs-on: ubuntu-latest
 
+    # The `get-vault-secrets` action only works when run from a `grafana`
+    # repository, so skip this test if the PR is from a different repository. We
+    # will still get a run of this workflow for the change before merging, as we
+    # use merge queues.
+    if: github.event_name != 'pull_request' || github.event.pull_request.head.repo.owner.login == 'grafana'
+
     steps:
       - name: Checkout code
         uses: actions/checkout@eef61447b9ff4aafe5dcd4e0bbf5d482be7e7871 # v4.2.1