Add changelog entry GitHub Action

.github/check-changelog-entry.sh

@@ -0,0 +1,7 @@
+#!/usr/bin/env bash
+
+# Fails if changelog_entry.yaml is empty or contains only whitespace
+if [ ! -s changelog_entry.yaml ] || ! grep -q '[^[:space:]]' changelog_entry.yaml; then
+  echo "changelog_entry.yaml is empty. Please add a changelog entry before merging."
+  exit 1
+fi

.github/workflows/pr_changelog.yaml

@@ -0,0 +1,14 @@
+name: Changelog entry
+on:
+  pull_request:
+    branches: [main]
+
+jobs:
+  require-entry:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+      - name: Ensure changelog entry exists
+        run: .github/check-changelog-entry.sh