.github/workflows: change natlab test trigger label (#19750)

The label "natlab" is a bit confusing and also used for other things.
Instead, change the trigger label to "run-natlab-tests".

Updates #13038

Signed-off-by: Claus Lensbøl <claus@tailscale.com>

.github/workflows/natlab-test.yml

@@ -4,7 +4,7 @@
 #
 # This workflow runs:
 #   - on demand (workflow_dispatch)
-#   - on PRs that carry the "natlab" label
+#   - on PRs that carry the "run-natlab-tests" label
 #   - on main, every 12 hours, via cron
 #
 # Layout:
@@ -40,7 +40,7 @@ jobs:
     if: |
       github.event_name == 'workflow_dispatch' ||
       github.event_name == 'schedule' ||
-      (github.event_name == 'pull_request' && contains(github.event.pull_request.labels.*.name, 'natlab'))
+      (github.event_name == 'pull_request' && contains(github.event.pull_request.labels.*.name, 'run-natlab-tests'))
     runs-on: ubuntu-latest
     timeout-minutes: 30
     outputs: