Update JPEG filetype from jpg to jpeg.

[n3011]

Pillow library does not have the _repr_jpg_ method. Recently the _repr_jpeg_ method is added python-pillow/Pillow#7135

[codecov]

Codecov Report

Merging #4904 (c9935db) into main (c85b49b) will decrease coverage by 0.19%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #4904      +/-   ##
==========================================
- Coverage   83.44%   83.25%   -0.19%     
==========================================
  Files         270      270              
  Lines       38153    38153              
==========================================
- Hits        31835    31764      -71     
- Misses       6318     6389      +71     

Flag	Coverage Δ
ui-tests	39.82% <100.00%> (-1.07%)	⬇️
unitexamples-tests	73.37% <100.00%> (-0.01%)	⬇️

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Impacted Files	Coverage Δ
panel/pane/image.py	87.00% <100.00%> (ø)

... and 10 files with indirect coverage changes

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[philippjfr]

Thanks _repr_jpeg_ is indeed the canonical form: https://ipython.readthedocs.io/en/stable/config/integrating.html#custom-methods

[philippjfr]

Thank you! Test failures are unrelated.