Fix workflow that automatically publishes @firebase/app (#5486)

Author: hsubox76

scripts/ci/add_changeset.ts

@@ -39,7 +39,11 @@ const FILE_PATH = `${projectRoot}/.changeset/bump-sdk-version.md`;
 async function addChangeSet() {
   // check if a few firebase version is being released
   try {
-    const { stdout } = await exec('yarn changeset status');
+    // The way actions/checkout works, there is no local `master` branch, but it
+    // has access to the remote origin/master.
+    const { stdout } = await exec(
+      'yarn changeset status --since origin/master'
+    );
     // only add a changeset for @firebase/app if
     // 1. we are publishing a new firebase version. and
     // 2. @firebase/app is not already being published