Fix doc build
Regression introduced in https://github.com/pytorch/pytorch/pull/73224
The caller for this script has never been updated to pass in main: https://github.com/pytorch/pytorch/blob/2ecc59086a5bc896c82f6f309d25569ec2933467/.github/workflows/_docs.yml#L81-L85
So this change made it so that all PR doc is built as-if it was a release (for example https://github.com/pytorch/pytorch/runs/6031182009?check_suite_focus=true) and so the coverage test for the doc didn't run for a month :(
Pull Request resolved: https://github.com/pytorch/pytorch/pull/75997
Approved by: https://github.com/musebc, https://github.com/seemethere
