Update upmsync.yml

Author: andnoonesthere

.github/workflows/upmsync.yml

@@ -9,7 +9,7 @@ jobs:
     runs-on: ubuntu-latest
     env:
       base: https://dl.google.com/games/registry/unity/com.google.firebase.database/com.google.firebase.database
-      version: 12.5.0
+      version: 12.6.0
     steps:
       - uses: actions/checkout@v2
       - name: Config