fix: load tabbed dash only for tests

[betodealmeida]

SUMMARY

The "tabbed dashboard" has no real content, but is the only dashboard where we tests tabs.

This PR removes the dashboard from a regular load-examples, keeping it only for tests.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

N/A

TESTING INSTRUCTIONS

Run superset load-examples and check that the "tabbed dashboard" is no longer there.
Run cypress tests and check that cypress/integration/dashboard/tabs.test.ts ran.

ADDITIONAL INFORMATION

• Has associated issue:
• Changes UI
• Includes DB Migration (follow approval process in SIP-59)
  • Migration is atomic, supports rollback & is backwards-compatible
  • Confirm DB migration upgrade and downgrade tested
  • Runtime estimates and downtime expectations provided
• Introduces new feature or API
• Removes existing feature or API

[codecov]

Codecov Report

Merging #16091 (845405c) into master (11a2d4d) will decrease coverage by 0.22%.
The diff coverage is 0.00%.

❗ Current head 845405c differs from pull request most recent head e1afde0. Consider uploading reports for the commit e1afde0 to get more accurate results

@@            Coverage Diff             @@
##           master   #16091      +/-   ##
==========================================
- Coverage   76.87%   76.64%   -0.23%     
==========================================
  Files         995      995              
  Lines       52876    52877       +1     
  Branches     6720     6720              
==========================================
- Hits        40647    40529     -118     
- Misses      12003    12122     +119     
  Partials      226      226              

Flag	Coverage Δ
hive	?
mysql	81.55% <0.00%> (-0.05%)	⬇️
postgres	81.61% <0.00%> (-0.01%)	⬇️
presto	?
python	81.70% <0.00%> (-0.44%)	⬇️
sqlite	81.21% <0.00%> (-0.01%)	⬇️

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

Impacted Files	Coverage Δ
...ponents/controls/VizTypeControl/VizTypeGallery.tsx	94.83% <ø> (ø)
...-frontend/src/visualizations/presets/MainPreset.js	0.00% <ø> (ø)
superset/cli.py	51.34% <0.00%> (-0.13%)	⬇️
superset/constants.py	100.00% <ø> (ø)
superset/db_engines/hive.py	0.00% <0.00%> (-82.15%)	⬇️
superset/db_engine_specs/hive.py	69.80% <0.00%> (-16.87%)	⬇️
superset/db_engine_specs/presto.py	83.47% <0.00%> (-6.91%)	⬇️
superset/views/database/mixins.py	81.03% <0.00%> (-1.73%)	⬇️
superset/connectors/sqla/models.py	88.08% <0.00%> (-1.67%)	⬇️
superset/db_engine_specs/base.py	87.98% <0.00%> (-0.39%)	⬇️
... and 4 more

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