Label PRs automatically as prerelease.

.github/labeler.yml

@@ -0,0 +1,2 @@
+prerelease:
+  - '*'

.github/workflows/pr_labeler.yml

@@ -0,0 +1,17 @@
+name: "Pull Request Labeler"
+
+on:
+  pull_request:
+    types: [opened]
+    branches: [main]
+
+jobs:
+  prerelease_labeler:
+    permissions:
+      contents: read
+      pull-requests: write
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/labeler@v4
+        with:
+          repo-token: "${{ secrets.GITHUB_TOKEN }}"