Add examples build workflow

Author: codingben

.github/workflows/box2d-examples-build.yml

@@ -0,0 +1,24 @@
+name: Box2D Examples Build
+
+on:
+  push:
+    branches: [v2.4]
+    paths:
+      - examples/**
+  pull_request:
+    branches: [v2.4]
+    paths:
+      - examples/**
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+      - name: Setup .NET Core
+        uses: actions/setup-dotnet@v1
+        with:
+          dotnet-version: "5.0.x"
+      - name: Build
+        run: dotnet build examples/ -c Release