Update actions/labeler pin to include actions/labeler#917 (#1971)

The previous pin (v6.0.1, 634933e) has a bug where labels added
by other workflows during the same run can be removed even with
sync-labels: false.  This caused Needs-Restricted-Paths-Review
to be stripped immediately after being applied (see #1967).

Pin to e52e4fb which includes the fix from actions/labeler#917
("Preserve manually added labels during workflow run and refine
label sync logic").

Author: leofang

.github/workflows/pr-auto-label.yml

@@ -20,4 +20,4 @@ jobs:
       pull-requests: write
     steps:
       - name: Apply labels
-        uses: actions/labeler@634933edcd8ababfe52f92936142cc22ac488b1b  # v6.0.1
+        uses: actions/labeler@e52e4fb63ed5cd0e07abaad9826b2a893ccb921f  # main (include actions/labeler#917)