Make tests stable on CI

[AlekSi]

Description

Also, remove https://github.com/FerretDB/FerretDB/labels/hacktoberfest until the next year.

Readiness checklist

• I added/updated unit tests (and they pass).
• I added/updated integration/compatibility tests (and they pass).
• I added/updated comments and checked rendering.
• I made spot refactorings.
• I updated user documentation.
• I ran task all, and it passed.
• I ensured that PR title is good enough for the changelog.
• (for maintainers only) I set Reviewers (@FerretDB/core), Milestone (Next), Labels, Project and project's Sprint fields.
• I marked all done items in this checklist.

[codecov]

Codecov Report

Merging #3678 (bc7a5b6) into main (051e963) will decrease coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #3678      +/-   ##
==========================================
- Coverage   76.38%   76.38%   -0.01%     
==========================================
  Files         321      321              
  Lines       22950    22950              
==========================================
- Hits        17531    17530       -1     
- Misses       4389     4390       +1     
  Partials     1030     1030              

see 9 files with indirect coverage changes

Flag	Coverage Δ
filter-true	72.36% <ø> (-0.04%)	⬇️
hana-1	3.57% <ø> (ø)
integration	72.36% <ø> (-0.04%)	⬇️
mongodb-1	5.43% <ø> (ø)
postgresql-1	52.28% <ø> (-0.12%)	⬇️
postgresql-2	51.71% <ø> (+<0.01%)	⬆️
postgresql-3	50.59% <ø> (ø)
sort-false	72.36% <ø> (-0.04%)	⬇️
sqlite-1	51.62% <ø> (-0.17%)	⬇️
sqlite-2	51.01% <ø> (+<0.01%)	⬆️
sqlite-3	49.83% <ø> (ø)
unit	29.92% <ø> (+0.03%)	⬆️

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