Ensure label check runs on all commits

From @larsoner in
numpy/numpydoc@12e59fd#r1298430414

Author: jarrodmillman

.github/workflows/label-check.yaml

@@ -4,8 +4,10 @@ on:
   pull_request:
     types:
       - opened
+      - reopened
       - labeled
       - unlabeled
+      - synchronize
 
 env:
   LABELS: ${{ join( github.event.pull_request.labels.*.name, ' ' ) }}

README.md

@@ -41,8 +41,10 @@ on:
   pull_request:
     types:
       - opened
+      - repoened
       - labeled
       - unlabeled
+      - synchronize
 
 env:
   LABELS: ${{ join( github.event.pull_request.labels.*.name, ' ' ) }}