Add “Check formatting” GitHub Actions workflow

.github/workflows/check-formatting.yml

@@ -0,0 +1,14 @@
+name: Check formatting
+on: push
+jobs:
+  check-formatting:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-java@v4
+        with:
+          distribution: zulu
+          java-version: 23
+      - run: |
+          curl -sSL -o ktfmt.jar https://github.com/facebook/ktfmt/releases/download/v0.53/ktfmt-0.53-jar-with-dependencies.jar
+          java -jar ktfmt.jar --dry-run --kotlinlang-style --set-exit-if-changed .