Fix pixel picker for square pixels

[maxnoe]

No description provided.

[codecov]

Codecov Report

Merging #1833 (5a517b4) into master (1b525d3) will increase coverage by 0.02%.
The diff coverage is 87.80%.

@@            Coverage Diff             @@
##           master    #1833      +/-   ##
==========================================
+ Coverage   91.80%   91.82%   +0.02%     
==========================================
  Files         190      190              
  Lines       15283    15298      +15     
==========================================
+ Hits        14030    14048      +18     
+ Misses       1253     1250       -3     

Impacted Files	Coverage Δ
ctapipe/instrument/camera/geometry.py	90.64% <75.00%> (-0.93%)	⬇️
ctapipe/visualization/mpl_camera.py	92.85% <96.00%> (+1.14%)	⬆️
ctapipe/utils/filelock.py	100.00% <0.00%> (+23.80%)	⬆️

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[LukasNickel]

Why was this done in the first place?
Did (x,y) refer to the pixel edges and not the centers?

[maxnoe]

Why was this done in the first place?
Did (x,y) refer to the pixel edges and not the centers?

For the old code using plt.Rectangle, (x, y) refered to the lower left corner. See changes here: #1819

https://matplotlib.org/stable/api/_as_gen/matplotlib.patches.Rectangle.html
https://matplotlib.org/stable/api/_as_gen/matplotlib.patches.RegularPolygon.html