exp save: Use pathspec to handle include_untracked.

[daavoo]

Closes #9061

[codecov]

Codecov Report

Base: 93.02% // Head: 93.01% // Decreases project coverage by -0.02% ⚠️

Coverage data is based on head (df6b485) compared to base (4720853).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #9064      +/-   ##
==========================================
- Coverage   93.02%   93.01%   -0.02%     
==========================================
  Files         457      457              
  Lines       36901    36912      +11     
  Branches     5338     5339       +1     
==========================================
+ Hits        34328    34334       +6     
- Misses       2054     2057       +3     
- Partials      519      521       +2     

Impacted Files	Coverage Δ
dvc/repo/experiments/save.py	95.23% <100.00%> (+0.23%)	⬆️
tests/func/experiments/test_save.py	100.00% <100.00%> (ø)
dvc/repo/experiments/queue/celery.py	85.92% <0.00%> (-1.86%)	⬇️

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