TST: fix some mpl warnings
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`

This change fixes `UserWarning` being emitted in tests calling `autocorrelation_plot`, `andrews_curves`, and `radviz`. 

`UserWarning` was caused by calling `plt.gca(xlim=..., ylim=...)` on a potentially already existing axis, so `matplotlib` warns about this forcing new axis creation. Solution was just to explicitly use `set_xlim` and `set_ylim` instead.

Does it make sense to also add to the relevant tests an assertion that no UserWarning is emitted to guarantee the new behavior?
Will add tests once #38620 is figured out > Will add tests once #38620 is figured out

hmm `tm.assert_produces_warning(None)`  should just work > > Will add tests once #38620 is figured out
> 
> hmm `tm.assert_produces_warning(None)` should just work

It wasn't raising even when a warning was returned, with examples of this given in the issue. So there are currently no failures in master when wrapping these plotting calls with `tm.assert_produces_warning(None)`, even though a warning is returned Wrapped existing calls that give warnings on master to avoid adding more plotting calls. If splitting out new tests for this is preferred instead, please let me know > Wrapped existing calls that give warnings on master to avoid adding more plotting calls. If splitting out new tests for this is preferred instead, please let me know

this looks good; ping on green Green thanks @mzeitlin11  @meeseeksdev backport 1.2.x