pr-labelsを指定しなかった場合のエラー修正 (#2094)

* pr-labelsを指定しなかった場合のエラー修正

* format修正 (#2095)

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

---------

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

Author: massongit

dist/update_pull_request.js

@@ -25,7 +25,9 @@ export async function script(
       await github.rest.pulls.update(pullsUpdateParams);
     }
 
-    const labels: string[] | undefined = process.env.PR_LABELS?.split(",");
+    const labels: string[] | undefined = process.env.PR_LABELS?.split(
+      ",",
+    ).filter((l) => l !== "");
 
     if (labels === undefined || labels.length === 0) {
       continue;