ci: Change release-please to GitHub Action (#374)

- release-please GitHub App is being turned down on August 15, 2025

Author: holtskinner

.github/release-please.yml

@@ -0,0 +1,19 @@
+on:
+  push:
+    branches:
+      - main
+
+permissions:
+  contents: write
+  pull-requests: write
+
+name: release-please
+
+jobs:
+  release-please:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: googleapis/release-please-action@v4
+        with:
+          token: ${{ secrets.A2A_BOT_PAT }}
+          release-type: python