flag_check: use project name instead of project path to determine the project

This avoids mistakenly misidentifying projects when they are not
checked out to the standard worktree.

Fixes: 340801952
Test: repo upload
Flag: NONE
Change-Id: I69835db39c48ef84e2c0a9bee1e4246aef3c22e3
Merged-In: I69835db39c48ef84e2c0a9bee1e4246aef3c22e3