Add GitHub workflows

.github/workflows/build.yml

@@ -0,0 +1,25 @@
+name: Build
+
+on:
+  push:
+    branches: [ main ]
+  pull_request:
+    branches: [ main ]
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+jobs:
+  build:
+    runs-on: windows-2022
+    steps:
+    - uses: actions/checkout@v3
+    - name: Setup dotnet
+      uses: actions/setup-dotnet@v3
+      with:
+        dotnet-version: |
+          7.0.x
+    - name: Build
+      run: |
+        dotnet build app/GHelper.sln