ci: add a separate native_backend_tests.yml, to run the native tests on all the available github actions vm environments

.github/workflows/native_backend_tests.yml

@@ -0,0 +1,26 @@
+name: native backend CI
+
+on:
+  push:
+    paths-ignore:
+      - "**.md"
+  pull_request:
+    paths-ignore:
+      - "**.md"
+
+concurrency:
+  group: build-ci-${{ github.event.pull_request.number || github.sha }}
+  cancel-in-progress: true
+
+jobs:
+  native-backend:
+    strategy:
+      matrix:
+        os: [ubuntu-18.04, ubuntu-20.04, macos-12, windows-2016, windows-2019, windows-2022]
+    runs-on: ${{ matrix.os }}
+    steps:
+      - uses: actions/checkout@v2
+      - name: Build V
+        run: make
+      - name: Test the native backend
+        run: ./v test vlib/v/gen/native/