fix: timeseries_heatmap

[tpuk0]

timeseries_heatmap from ydata_profiling.visualisation.plot drops an error, when 'entity_column' is of type str.
The reason for this is that the arguments to pivot_table are passed in the wrong order - see documentation.

Existing unit test does not cover a case where entities are strings, thus the bug was missed.

[fabclmnt]

HI @tpuk0 ,

thank you for your contribution! The team will be reviewing your PR shortly :)

[codecov]

Codecov Report

Attention: Patch coverage is 85.71429% with 1 line in your changes missing coverage. Please review.

Project coverage is 90.09%. Comparing base (3d4e482) to head (16e2585).
Report is 76 commits behind head on develop.

Files	Patch %	Lines
src/ydata_profiling/visualisation/plot.py	66.66%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1601      +/-   ##
===========================================
+ Coverage    90.01%   90.09%   +0.07%     
===========================================
  Files          194      196       +2     
  Lines         6368     6438      +70     
===========================================
+ Hits          5732     5800      +68     
- Misses         636      638       +2     

Flag	Coverage Δ
py3.8-ubuntu-22.04-pandas	90.09% <85.71%> (+0.07%)	⬆️

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