Fix nModified count for update's $set operator with the same value

[w84thesun]

Description

This PR closes #571.

Readiness checklist

• I added tests for new functionality or bugfixes.
• I ran task all, and it passed.
• I added/updated comments for both exported and unexported top-level declarations (functions, types, etc).
• I checked comments rendering with task godocs.
• (for maintainers only) I set Reviewers, Assignee, Labels, Project and project's Sprint fields.
• I marked all done items in this checklist.

[codecov]

Codecov Report

Merging #949 (1a7ebf9) into main (0a45d81) will decrease coverage by 0.02%.
The diff coverage is 62.50%.

@@            Coverage Diff             @@
##             main     #949      +/-   ##
==========================================
- Coverage   61.97%   61.95%   -0.03%     
==========================================
  Files         228      228              
  Lines       10591    10597       +6     
==========================================
+ Hits         6564     6565       +1     
- Misses       3252     3255       +3     
- Partials      775      777       +2     

Impacted Files	Coverage Δ
internal/handlers/common/update.go	85.61% <62.50%> (-0.42%)	⬇️
internal/util/version/version.go	55.00% <0.00%> (-5.00%)	⬇️
internal/handlers/pg/pgdb/collections.go	57.52% <0.00%> (-2.66%)	⬇️
internal/handlers/pg/msg_dbstats.go	72.09% <0.00%> (+6.97%)	⬆️

Flag	Coverage Δ
integration	56.67% <62.50%> (+<0.01%)	⬆️
mongodb	18.61% <0.00%> (-0.07%)	⬇️
pg	61.62% <62.50%> (+<0.01%)	⬆️
tigris	18.25% <0.00%> (+0.04%)	⬆️
unit	24.27% <0.00%> (-0.53%)	⬇️

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