Update and rename main.yml to require-label.yml

.github/workflows/require-label.yml

+name: Require PR label
+
+on: [pull_request]
+
+jobs:
+  require-label:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: yogevbd/require-label-action@master
+      with:
+        valid-labels: ["bug", "enhancement", "feature"]