Fully overwrite values in MillingStep entry upon update

[tieneupin]

Now that the FIB milling progress registration logic is live, we have been able to start detecting bugs that weren't caught during testing.

In the FIB AutoTEM metadata, once a step is complete, the is_enabled field is set back to False. However, the current ISPyB insertion logic only supports the insertion and updating of truth-y values. Once the field is set to True, it can't be set back to False again based on current logic.

This PR fixes that by fully overwriting all values in an existing MillingStep database entry when updating it, instead of updating the value only when it's truth-y.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 53.11%. Comparing base (df053f5) to head (146a09b).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #832   +/-   ##
=======================================
  Coverage   53.11%   53.11%           
=======================================
  Files         100      100           
  Lines       10834    10834           
  Branches     1434     1434           
=======================================
  Hits         5754     5754           
  Misses       4775     4775           
  Partials      305      305           

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[tieneupin]

Discussed and not needed. It's more practical to have a record of steps that were previously enabled than it is to fully follow the metadata.