workflows/labels: fix approved-by-maintainer label

Due to a type mismatch, maintainer approvals were never counted as such.
The API returns integers for the user IDs, but the JSON file has strings
as object keys.

(cherry picked from commit 25a0ee0817)

.github/workflows/labels.yml

@@ -166,7 +166,7 @@ jobs:
 
                   const maintainers = new Set(Object.keys(
                     JSON.parse(await readFile(`${pull_request.number}/maintainers.json`, 'utf-8'))
-                  ))
+                  ).map(m => Number.parseInt(m, 10)))
 
                   // And the labels that should be there
                   const after = JSON.parse(await readFile(`${pull_request.number}/changed-paths.json`, 'utf-8')).labels