ci: allow campaigner-automated-change label (#11311)

ci: allow `campaigner-automated-change` label

The PR label-validation workflow only accepts labels matching one of a
small set of category prefixes (`type:`, `comp:`, `inst:`, `tag:`, ...).
Labels applied by external automation (e.g. Campaigner) don't follow
that scheme, so they trip the check and the PR gets a sticky blocking
comment that requires a maintainer to remove.

Add an explicit exact-match allowlist alongside the prefix list so
known-good labels from automation tooling can pass without conflating
the "category prefix" concept with "exact label name".

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Co-authored-by: devflow.devflow-routing-intake <devflow.devflow-routing-intake@kubernetes.us1.ddbuild.io>

Author: mhlidd

.github/workflows/check-pull-request-labels.yaml

@@ -141,6 +141,11 @@ jobs:
               'performance:',  // To refactor to 'ci: ' in the future
               'run-tests:'     // Unused since GitLab migration
             ]
+            // Exact-match labels that don't fit a category prefix (e.g. labels applied
+            // by external automation tooling).
+            const exactAllowlist = [
+              'campaigner-automated-change'
+            ]
             // Re-fetch labels only if the previous step modified them (ex: "Bits AI" removal)
             let prLabels
             if (process.env.LABELS_STALE === 'true') {
@@ -156,7 +161,10 @@ jobs:
             // Look for invalid labels
             const invalidLabels = prLabels
               .map(label => label.name)
-              .filter(label => validCategories.every(prefix => !label.startsWith(prefix)))
+              .filter(label =>
+                !exactAllowlist.includes(label) &&
+                validCategories.every(prefix => !label.startsWith(prefix))
+              )
             const hasInvalidLabels = invalidLabels.length > 0
             // Get existing comments to check for blocking comment
             const comments = await github.rest.issues.listComments({