Move find and aggregation cursor integration tests to getMore

[chilagrow]

Description

Closes #1733.

• Moves TestQueryBatchSize from query_test.go to TestGetMoreCommand in getmore_test.go
• Merges TestQueryBatchSize in query_test.go and TestAggregateBatchSize in aggregate_documents_test.go to TestGetMoreBatchSizeCursor in getmore_test.go

Readiness checklist

• I added/updated unit tests.
• I added/updated integration/compatibility tests.
• 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), Labels, Project and project's Sprint fields.
• I marked all done items in this checklist.

[codecov]

Codecov Report

Merging #2952 (54a83a6) into main (f939bd2) will decrease coverage by 0.07%.
The diff coverage is n/a.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2952      +/-   ##
==========================================
- Coverage   64.05%   63.98%   -0.07%     
==========================================
  Files         451      451              
  Lines       24107    24107              
==========================================
- Hits        15441    15425      -16     
- Misses       7704     7718      +14     
- Partials      962      964       +2     

see 3 files with indirect coverage changes

Flag	Coverage Δ
integration	57.29% <ø> (-0.11%)	⬇️
mongodb	?
pg	57.29% <ø> (-0.04%)	⬇️
shard-1	42.44% <ø> (+0.51%)	⬆️
shard-2	45.61% <ø> (+3.34%)	⬆️
shard-3	41.48% <ø> (-4.60%)	⬇️
unit	24.23% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

[w84thesun]

LGTM!

[rumyantseva]

LGTM