fix: correct Flutter setup parameters in SDK update workflow

Author: pvditto

.github/workflows/update-sdk-versions.yml

@@ -45,7 +45,8 @@ jobs:
       - name: Setup Flutter
         uses: subosito/flutter-action@v2
         with:
-          flutter-version: "stable"
+          channel: "stable"
+          cache: true
 
       - name: Setup Rust
         uses: dtolnay/rust-toolchain@stable