CI/DOC: replace master -> main branch
Follow-up on https://github.com/pandas-dev/pandas/issues/39577
This has failed a few times it appears. Not sure why this PR would influence this failure:

https://dev.azure.com/pandas-dev/pandas/_build/results?buildId=72190&view=logs&j=c4a134e2-1a49-5486-5bb3-f47b2d22370f&t=a5a6d308-4ac5-5e83-907a-cda493e43b7d&l=49 do we need to backport this? (yes?) > do we need to backport this? (yes?)

I would think so. thanks @jorisvandenbossche  @meeseeksdev backport 1.4.x Something went wrong ... Please have a look at my logs. The backport is actually already done at https://github.com/pandas-dev/pandas/pull/45338 by meeseeksdev (not fully sure why he mentioned here that "something went wrong") because @jreback triggered manually. The bot sometimes does not pick it up (although not noticed this lately)
 yeah i always trigger (though i realiE i don't really need to) > yeah i always trigger (though i realiE i don't really need to)

yeah probably safer to make sure nothing gets missed. If the PR has a release note then I check release notes are in sync so these won't get missed. If if fixes ci then again won't get missed as the ci would be failing on the backport branch. If it's a doc fix or some other cleanup then could potentially be missed if the bot does not pick it up and it is not triggered manually.