Backport PR #40718 on branch 1.2.x (COMPAT: matplotlib 3.4.0)
Backport PR #40718: COMPAT: matplotlib 3.4.0
hmm didn't completely fix things, cc @simonjayhawkins  > hmm didn't completely fix things, cc @simonjayhawkins

will look at this (and other backport PR) later today/tomorrow (currently running benchmarks https://github.com/pandas-dev/pandas/pull/40725#issuecomment-812468736) other warnings should be fixed in #40801