Test for exporting annotations into CS folder

[klakhov]

Motivation and context

Test for #6265

How has this been tested?

Checklist

• I submit my changes into the develop branch
• I have added a description of my changes into the CHANGELOG file
• I have updated the documentation accordingly
• I have added tests to cover my changes
• I have linked related issues (see GitHub docs)
• I have increased versions of npm packages if it is necessary
  (cvat-canvas,
  cvat-core,
  cvat-data and
  cvat-ui)

License

• I submit my code changes under the same MIT License that covers the project.
  Feel free to contact the maintainers if that's a concern.

[codecov]

Codecov Report

Merging #6301 (3838a65) into develop (9a600f3) will decrease coverage by 1.68%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           develop    #6301      +/-   ##
===========================================
- Coverage    74.78%   73.10%   -1.68%     
===========================================
  Files          145      289     +144     
  Lines        16934    35695   +18761     
  Branches      3285     3480     +195     
===========================================
+ Hits         12664    26096   +13432     
- Misses        4264     9593    +5329     
  Partials         6        6              

Components	Coverage Δ
cvat-ui	75.06% <ø> (+0.27%)	⬆️
cvat-server	71.18% <ø> (∅)