firebase-ios-sdk

Enable GHA for GDT and GDTCCT (#4780)

* Enable GHA for GDT and GDTCCT

* Fix run syntax

* No capital OS letters

* Add a retry.sh to replicate travis_retry functionality

* Rearrange the jobs and use needs:

* Call retry.sh with the correct syntax

* An additional needs:

* Use the retry we already have

* Factor iOS, macOS, and tvOS into separate jobs, move comprehensive jobs to cron

* Set cron jobs to need the base jobs

* Change back to pull_request from check_run

* Fix typo

* I just can't stop making typos