[tpoliaw]

If the extension is not present the instrument name is used so setting
the extension to the same value doesn't make sense and is skipped.

Skipping the update entirely led to two issues:

• if the extension had previously been set to a new value it couldn't be
  set back
• if resetting the extension was the only update being made, it would
  lead to invalid SQL and an error.

Instead of skipping the field entirely in the case that it matches the
instrument, use None and reset the DB value to NULL to rely on the
instrument being the default.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.50%. Comparing base (8abe464) to head (7a5f2b4).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #314      +/-   ##
==========================================
+ Coverage   79.34%   79.50%   +0.15%     
==========================================
  Files          13       13              
  Lines        2116     2132      +16     
==========================================
+ Hits         1679     1695      +16     
  Misses        437      437              

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