suppress default branch name warning

[eugenesvk]

Github actions warn you when you use the default git init with the default branch name as it may change in the future, but you have master hardcoded later, so changing defaults will break the workflow

I've added an explicit name so that even when the default changes, that won't break the workflow

Picked a less common gh_action name as the previous master confused me when trying a few options, I thought it was bugged because my site's repo's branch was main (I realized later that the branch name is irrelevant, a non master/main name would've helped, so I picked one here)