chore: Fixed unstable Bubbles cypress test

[adam-stasiak]

SUMMARY

I changed test to not rely on constant 214 number of bubbles but on value directly from xhr response -> Then we verify the UI.
I observed that one bubble in the most right side is not fully visible - > that's why I placed 'exist' instead of 'visible'. maybe good idea to extend area of chart for smaller resolutions?

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

TEST PLAN

ADDITIONAL INFORMATION

• Has associated issue:
• Changes UI
• Requires DB Migration.
• Confirm DB Migration upgrade and downgrade tested.
• Introduces new feature or API
• Removes existing feature or API

[codecov-io]

Codecov Report

Merging #11583 into master will decrease coverage by 4.40%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #11583      +/-   ##
==========================================
- Coverage   66.60%   62.20%   -4.41%     
==========================================
  Files         876      876              
  Lines       42146    42139       -7     
  Branches     3943     3943              
==========================================
- Hits        28070    26211    -1859     
- Misses      13973    15746    +1773     
- Partials      103      182      +79     

Flag	Coverage Δ
cypress	?
javascript	62.56% <ø> (ø)
python	61.97% <ø> (-0.18%)	⬇️

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

Impacted Files	Coverage Δ
superset-frontend/src/SqlLab/App.jsx	0.00% <0.00%> (-100.00%)	⬇️
superset-frontend/src/explore/App.jsx	0.00% <0.00%> (-100.00%)	⬇️
superset-frontend/src/dashboard/App.jsx	0.00% <0.00%> (-100.00%)	⬇️
superset-frontend/src/explore/index.jsx	0.00% <0.00%> (-100.00%)	⬇️
superset-frontend/src/dashboard/index.jsx	0.00% <0.00%> (-100.00%)	⬇️
superset-frontend/src/setup/setupColors.js	0.00% <0.00%> (-100.00%)	⬇️
superset-frontend/src/chart/ChartContainer.jsx	0.00% <0.00%> (-100.00%)	⬇️
superset-frontend/src/setup/setupFormatters.js	0.00% <0.00%> (-100.00%)	⬇️
superset-frontend/src/explore/reducers/index.js	0.00% <0.00%> (-100.00%)	⬇️
superset-frontend/src/setup/setupPluginsExtra.js	0.00% <0.00%> (-100.00%)	⬇️
... and 182 more

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