[GH] Limit Firebase Tests to the main repository
[GH] Limit Firebase Tests to the main repository

FTL authentication only exists for the main repo hence don't run them in forks.

Bug: n/a
Test: CI

This is an imported pull request from https://github.com/androidx/androidx/pull/168.

Resolves #168
Github-Pr-Head-Sha: 0e83c5067d506e791c1de33e8a7126a317d50562
GitOrigin-RevId: eb5101ffb14a46e38ac74bcf296bb6965be56630
Change-Id: Ic123f5773524dc877c66e4e6b5ae4aead38bc0fe

androidx/androidx,androidx/androidx,androidx/androidx,AndroidX/androidx,AndroidX/androidx,AndroidX/androidx,AndroidX/androidx,AndroidX/androidx,AndroidX/androidx,AndroidX/androidx,AndroidX/androidx,androidx/androidx,androidx/androidx,AndroidX/androidx,androidx/androidx,androidx/androidx,androidx/androidx,androidx/androidx,AndroidX/androidx,androidx/androidx