actions: automatically remove waiting label from PRs on synchronize

there are probably other conditions where we'd want to remove this, but this will do for now.

.github/workflows/pr-remove-waiting-label.yml

@@ -0,0 +1,24 @@
+name: Remove waiting label from PRs
+
+on:
+  pull_request_target:
+    types: synchronize
+
+jobs:
+  delabel:
+    name: Remove label
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Remove label
+        uses: actions/github-script@v7
+        with:
+          github-token: ${{ github.token }}
+          script: |
+            const [owner, repo] = context.payload.repository.full_name.split('/');
+            await github.rest.issues.removeLabel({
+              owner: owner,
+              repo: repo,
+              issue_number: context.payload.number,
+              name: "Status: Waiting on Author",
+            });