This Replicates the functionality of our Jenkins test-pr job (#2031)

move Jenkins pr testing to GitHub actions.

uses same logic for detecting changes in PR.

requires runner with public label

.github/workflows/testpr.yml

@@ -0,0 +1,46 @@
+name: build pr kernel
+# This workflow is triggered on pushes to the repository.
+on: [pull_request]
+
+jobs:
+  build:
+    name: Compile changed kernel
+    # This job runs on self hosted Linux machine, with public label
+    runs-on: [self-hosted, public]
+    steps:
+#      - uses: rokroskar/workflow-run-cleanup-action@v0.2.2
+#        env:
+#          GITHUB_TOKEN: "${{ secrets.GITHUB_TOKEN }}"
+      - uses: actions/checkout@v2
+        with:
+          fetch-depth: 0
+          path: build
+          clean: false
+      - uses: actions/checkout@v2
+        with:
+          repository: armbian/ci-testing-tools
+          path: ci-testing-tools
+      - name: Find SBC target and build kernel
+        shell: bash {0}         
+        run: |  
+         cd build
+         GIT_COMMIT=$(echo $GITHUB_SHA)
+         GIT_PREVIOUS_COMMIT=$(git rev-parse origin/$GITHUB_BASE_REF)
+         ARMBIAN_BOARD=tritium-h5
+         ARMBIAN_BRANCH=current
+         cd ..
+         env
+         source ci-testing-tools/jenkins_ci.sh
+         
+         mkdir -p build/userpatches
+         cp -f ci-testing-tools/config-jenkins-kernel.conf build/userpatches/
+         configure_monorepo_watcher
+         generate_board_table
+         load_board_table
+         cd build
+         get_files_changed
+         get_build_target
+         git checkout ${GITHUB_SHA}
+         git branch -v
+         export GPG_TTY=$(tty)
+         build_kernel jenkins-kernel