use single quotes for string literals, fixes #2001

[cldellow]

This modernizes some uses of double quotes for string literals to use only single quotes, fixes #2001

While developing it, I manually enabled the stricter mode by using the code snippet at https://gist.github.com/cldellow/85bba507c314b127f85563869cd94820

I think that code snippet isn't generally safe/portable, so I haven't tried to automate it in the tests.

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📚 Documentation preview 📚: https://datasette--2004.org.readthedocs.build/en/2004/

[codecov]

Codecov Report

Base: 92.11% // Head: 92.11% // No change to project coverage 👍

Coverage data is based on head (dca7634) compared to base (e4ebef0).
Patch has no changes to coverable lines.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2004   +/-   ##
=======================================
  Coverage   92.11%   92.11%           
=======================================
  Files          38       38           
  Lines        5555     5555           
=======================================
  Hits         5117     5117           
  Misses        438      438           

Impacted Files	Coverage Δ
datasette/utils/__init__.py	94.86% <ø> (ø)

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