update: prevent re-download on every update

[dtrifiro]

fixes #8751

[codecov]

Codecov Report

Base: 93.51% // Head: 93.52% // Increases project coverage by +0.00% 🎉

Coverage data is based on head (7c07050) compared to base (a24c389).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #8752   +/-   ##
=======================================
  Coverage   93.51%   93.52%           
=======================================
  Files         457      457           
  Lines       36249    36282   +33     
  Branches     5257     5262    +5     
=======================================
+ Hits        33899    33933   +34     
  Misses       1843     1843           
+ Partials      507      506    -1     

Impacted Files	Coverage Δ
dvc/stage/imports.py	87.50% <100.00%> (+1.78%)	⬆️
tests/func/test_update.py	100.00% <100.00%> (ø)
tests/unit/stage/test_stage.py	100.00% <100.00%> (ø)

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[dberenbaum]

Seems like the behavior between --no-download and --to-remote is inconsistent. We can fix in this PR or follow up with another one. For --to-remote, the outs metadata is updated with the new info but the workspace remains untouched, while --no-download drop the outs metadata and deletes anything in the workspace.

[dtrifiro]

Regarding --to-remote and --no-download, I think we can follow up later.