feat: Add pph checker

Adds a github action which runs the pph script and checks if this introduces changes.

Author: erikzenker

.github/workflows/pph-checker.yml

@@ -0,0 +1,19 @@
+name: Pph Checker
+
+on:
+  push:
+    branches: [ master ]
+  pull_request:
+    branches: [ master ]
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v2
+    - name: Run pph
+      run: ./tools/pph.sh
+    - name: Check diff
+      run: git diff --exit-code