fix(mbsync): do not clear metadata if import.from_scratch is set

[ShimmerGlass]

Description

if import.from_scratch was set in the config, runnning mbsync would clear any metadata not provided by MBz (replay gain, lyrics, genres...). we now ignore this setting when running mbsync to preserve metadata.

Fixes: #6613

To Do

• Documentation. (If you've added a new command-line flag, for example, find the appropriate page under docs/ to describe it.)
• Changelog. (Add an entry to docs/changelog.rst to the bottom of one of the lists near the top of the document.)
• Tests. (Very much encouraged but not strictly required.)

[codecov]

Codecov Report

❌ Patch coverage is 90.90909% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 72.39%. Comparing base (0309096) to head (65ccaf1).

Files with missing lines	Patch %	Lines
beetsplug/bpsync.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #6625   +/-   ##
=======================================
  Coverage   72.38%   72.39%           
=======================================
  Files         159      159           
  Lines       20645    20649    +4     
  Branches     3269     3270    +1     
=======================================
+ Hits        14944    14948    +4     
  Misses       4976     4976           
  Partials      725      725           

Files with missing lines	Coverage Δ
beets/autotag/hooks.py	98.90% <100.00%> (+0.01%)	⬆️
beetsplug/mbsync.py	82.50% <100.00%> (ø)
beetsplug/bpsync.py	21.83% <0.00%> (ø)

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[snejus]

Thanks for addressing this. I agree that we should ignore import.from_scratch configuration when we synchronise data.

I've seen multiple new issues and discussions created due to this problem, so this has definitely been causing confusion to people.

Maybe worth updating bpsync plugin as well, for consistency?

[ShimmerGlass]

@snejus done