fix(months): monthClassName is passed the month instead of the current day

[DanielSharp01]

This PR aims to fix a bug with monthClassName in the month picker. The bug was that the current date with the selected year is passed for all months making the feature not be able to target specific months only all of them in a given year.

The use case is something like this:

This might need some tests, however I don't exactly know where to add them. Given a bit of guidance I'm happy to contribute those as well.

[codecov[bot]]

Codecov Report

Merging #3709 (aa2394b) into master (60d95bb) will not change coverage. The diff coverage is 50.00%.

@@           Coverage Diff           @@
##           master    #3709   +/-   ##
=======================================
  Coverage   94.08%   94.08%           
=======================================
  Files          20       20           
  Lines        1723     1723           
  Branches      417      417           
=======================================
  Hits         1621     1621           
  Misses         31       31           
  Partials       71       71           

Impacted Files	Coverage Δ
src/month.jsx	92.64% <50.00%> (ø)

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