ci: add mirroring to codeberg

Author: AstreaTSS

.github/workflows/mirror.yml

@@ -0,0 +1,16 @@
+name: "Mirror Repository"
+
+on: [push]
+
+jobs:
+  mirror:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+        with:
+          fetch-depth: 0
+      - uses: yesolutions/mirror-action@master
+        with:
+          REMOTE: 'https://codeberg.org/Stellarium-Labs/StellariumLabsBot.git'
+          GIT_USERNAME: Astrea
+          GIT_PASSWORD: '${{ secrets.CODEBERG_PASSWORD }}'