Add a build action

.gitea/workflows/build.yaml

@@ -0,0 +1,23 @@
+name: Build
+
+on:
+  push:
+    branches:
+      - '**'
+  pull_request:
+    branches: [master]
+
+jobs:
+  build:
+    runs-on: alpine
+    steps:
+      - name: Set up environment
+        shell: ash {0}
+        run: |
+          apk -U upgrade
+          apk add --no-cache git bash cmake build-base ninja
+      - uses: actions/checkout@v4
+      - name: Build
+        run: |
+          cmake -B build -G Ninja
+          ninja -C build