workflows: set up mirror to GitLab (#173)

see https://gitlab.com/markus-wa/demoinfocs-golang

Author: markus-wa

.github/workflows/mirror.yml

@@ -0,0 +1,15 @@
+name: Mirror
+on: [push]
+
+jobs:
+  build:
+    name: Mirror to GitLab
+    runs-on: ubuntu-latest
+    steps:
+      - name: Mirror to GitLab
+        uses: wearerequired/[email protected]
+        env:
+          SSH_PRIVATE_KEY: ${{ secrets.SSH_PRIVATE_KEY }}
+        with:
+          source-repo: '[email protected]:markus-wa/demoinfocs-golang.git'
+          destination-repo: '[email protected]:markus-wa/demoinfocs-golang.git'