Fix building assets on breeze start-airflow (#15663)

Error because `webpack` is not install because `yarn install --frozen-lockfile` is not run:

```
root@f5fc5cfc9a43:/opt/airflow# cd /opt/airflow/airflow/www/; yarn dev
yarn run v1.22.5
$ NODE_ENV=dev webpack --watch --colors --progress --debug --output-pathinfo --devtool eval-cheap-source-map -
-mode development
/bin/sh: 1: webpack: not found
error Command failed with exit code 127.
info Visit https://yarnpkg.com/en/docs/cli/run for documentation about this command.
root@f5fc5cfc9a43:/opt/airflow/airflow/www#
```

This commits adds `yarn install --frozen-lockfile` to the command which fixes it.

This was missed in https://github.com/apache/airflow/pull/13313/files

GitOrigin-RevId: 60a3da6fecdaa90c41a4fed1d4c8b6c7754b4968

scripts/in_container/bin/run_tmux

@@ -54,7 +54,7 @@ tmux send-keys 'airflow webserver' C-m
 if [[ -z "${USE_AIRFLOW_VERSION=}" ]]; then
     tmux select-pane -t 0
     tmux split-window -h
-    tmux send-keys 'cd /opt/airflow/airflow/www/; yarn dev' C-m
+    tmux send-keys 'cd /opt/airflow/airflow/www/; yarn install --frozen-lockfile; yarn dev' C-m
 fi
 
 # Attach Session, on the Main window