fix update-node-modules-cache workflow (#45547)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/45547

Was missing the step to checkout the repo before running yarn.

Changelog: [Internal]

Reviewed By: sammy-SC, realsoelynn

Differential Revision: D59979543

fbshipit-source-id: 2ab52efbc655cb6ff7b6544ff3939c019c5d45a6