chore(ci): checkout files when updating package-lock (#28778)

In https://github.com/ionic-team/ionic-framework/pull/28697 I moved the
package-lock work to its own step to lets us re-run that if it fails.
However, I forgot to checkout the project files in that step, so there
was no `package-lock.json` file to update [resulting in an
error](https://github.com/ionic-team/ionic-framework/actions/runs/7398703880/job/20128761433).