Added actions/labeler

Merged: https://github.com/ruby/ruby/pull/12609

.github/labeler.yml

@@ -0,0 +1,6 @@
+Documentation:
+- changed-files:
+  - any-glob-to-any-file: doc/**
+
+Backport:
+- base-branch: 'ruby_3_\d'

.github/workflows/labeler.yml

@@ -0,0 +1,12 @@
+name: "Pull Request Labeler"
+on:
+- pull_request_target
+
+jobs:
+  labeler:
+    permissions:
+      contents: read
+      pull-requests: write
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/labeler@v5