Add build.yml Forgejo workflow

.forgejo/workflows/build.yml

@@ -0,0 +1,16 @@
+on: [pull_request]
+jobs:
+    build:
+        runs-on: docker
+        container:
+            image: forge.a-lec.org/speed-dreams/debian-sd:stable
+        steps:
+            - run: |
+                git clone \
+                    -b ${{ env.GITHUB_HEAD_REF }} \
+                    --depth 1 \
+                    ${{ env.GITHUB_SERVER_URL }}/${{ env.GITHUB_REPOSITORY }}.git \
+                    src
+                cd src/
+                cmake -B build -DSD_ASSUME_DATADIR=1
+                cmake --build build -j$(nproc --all)