ci(AppCheck): use env_vars input in sdk.appcheck.yml for remote branch

Author: ncooke3

.github/workflows/sdk.appcheck.yml

@@ -30,6 +30,8 @@ jobs:
     uses: ./.github/workflows/_spm.yml
     with:
       target: ${{  matrix.target }}
+      env_vars: '{"FIREBASE_APP_CHECK_BRANCH": "nc/target-split"}'
+
 
   catalyst:
     uses: ./.github/workflows/_catalyst.yml