fix #5340: before merging gather only xrefs of changes with status pending on originating tree

[BertKoor]

fixes #5340

XREFs of changes with status accepted or rejected in the originating tree should not be queried for prior to a tree merge.
The merge itself does nothing with pending changes in the originating tree.

XREFs of pending changes could be useful to gather though. If these overlap, then the merge will ask to first execute renumbering this tree. Then renumbering won't execute while there are still pending changes:
https://github.com/fisharebest/webtrees/blob/main/app/Http/RequestHandlers/RenumberTreeAction.php#L59-L68

You need to accept or reject all pending changes before proceeding.

With all changes being accepted or rejected, renumbering will take care of any colliding XREFs and there should be no issue with merging.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 35.37%. Comparing base (c0f97f5) to head (91a704a).
⚠️ Report is 11 commits behind head on main.

Files with missing lines	Patch %	Lines
app/Services/AdminService.php	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #5342      +/-   ##
============================================
- Coverage     35.37%   35.37%   -0.01%     
  Complexity    11196    11196              
============================================
  Files          1166     1166              
  Lines         48031    48032       +1     
============================================
  Hits          16990    16990              
- Misses        31041    31042       +1     

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