Add missing project to .firebaserc (#758)

To enable GitHub workflow deployment again.
diff --git a/.firebaserc b/.firebaserc
index c88e8a2..0e582ba 100644
--- a/.firebaserc
+++ b/.firebaserc
@@ -1,4 +1,7 @@
 {
+  "projects": {
+    "gallery": "gallery-flutter-dev"
+  },
   "targets": {
     "gallery-flutter-dev": {
       "hosting": {
@@ -11,4 +14,4 @@
       }
     }
   }
-}
\ No newline at end of file
+}