Switch barplot tests from ci to errorbar

[stefmolin]

I noticed that running the test_categorical.py file prints out a lot of FutureWarnings (see below for some examples), which aren't being checked for the in the tests themselves. Since the ci parameter is being deprecated in barplot() (#2866), I updated these tests to use errorbar as indicated in the FutureWarning. There were also cases of palette being provided without hue, which I addressed as well.

tests/test_categorical.py::TestBarPlotter::test_unaligned_index
  /Users/stefanie/seaborn/tests/test_categorical.py:2357: FutureWarning:

  The `ci` parameter is deprecated. Use `errorbar='sd'` for the same effect.

    cat.barplot(x=self.g, y=self.y, ci="sd", ax=ax1)

tests/test_categorical.py::TestCatPlot::test_plot_colors
  /Users/stefanie/seaborn/tests/test_categorical.py:2905: FutureWarning: Passing `palette` without assigning `hue` is deprecated.
    g = cat.catplot(x="g", y="y", data=self.df, palette="Set2")

[codecov]

Codecov Report

Merging #2949 (18eb6fe) into master (ae9080d) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #2949   +/-   ##
=======================================
  Coverage   98.30%   98.31%           
=======================================
  Files          69       69           
  Lines       23004    23030   +26     
=======================================
+ Hits        22615    22641   +26     
  Misses        389      389           

Impacted Files	Coverage Δ
seaborn/axisgrid.py	97.20% <100.00%> (+0.01%)	⬆️
tests/test_axisgrid.py	99.38% <100.00%> (+0.01%)	⬆️
tests/test_categorical.py	99.77% <100.00%> (ø)

[mwaskom]

Thanks @stefmolin this is super helpful