Import all no longer deletes mapped items

[isc-pbarton]

Description

Fixes #997
A more general approach is in #1003 but I'm unsure if we want it. Skipping deletion of mapped items on import is a more targeted and less risky fix to the major bug in #997.

Testing

Unit test covers the scenario in the bug report

Checklist

• This branch has the latest changes from the main branch rebased or merged.
• [N/A] Web UI has been built (any changes in git-webui/src have matching changes in git-webui/release)
• CHANGELOG.md entry added if appropriate.
• [N/A] Documentation has been/will be updated

[codecov-commenter]

Codecov Report

❌ Patch coverage is 25.00000% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 49.95%. Comparing base (0290792) to head (4203052).

Files with missing lines	Patch %	Lines
cls/SourceControl/Git/Utils.cls	25.00%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1004      +/-   ##
==========================================
+ Coverage   49.92%   49.95%   +0.02%     
==========================================
  Files          23       23              
  Lines        3373     3375       +2     
==========================================
+ Hits         1684     1686       +2     
  Misses       1689     1689              

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