ENH: dont guess %Y/%m
Follow-up from https://github.com/pandas-dev/pandas/pull/49389

Guess "year month", but only if it's "%Y-%m" as that's ISO8601 compliant
The goal would still be to guess most date formats, especially non-ISO8601 ones

It's just for dates which don't have all three of "year, month, and day" that perhaps it's better to not guess (unless they're ISO8601), cc @WillAyd  Yea I think adhering to ISO for inference is going to be the easiest to develop / communicate. Thanks @MarcoGorelli 