Sort extensions alphabetically in error message

[radarhere]

Suggestions for python-pillow#8338

• I figured out how to use tempfile.NamedTemporaryFile for the other test as well
• In "cannot find glyph data file {root}.{{png|gif|pbm}}", I suggest sorting the extensions alphabetically
• You can see what the docs look like for your PR at https://pillow--8338.org.readthedocs.build/en/8338/reference/ImageFont.html#PIL.ImageFont.load.
  
  As a user, I look at the

See also PIL.ImageFont.truetype()

and react with 'Yes, I know, I can see it right there below'. So my suggestion instead is

For loading TrueType or OpenType fonts instead, see truetype().