fix: Invalid references in the basic template

[michael-s-molina]

SUMMARY

Fixes invalid references in superset/templates/superset/basic.html which were generating the following 404 errors:

GET http://localhost:9000/static/appbuilder/datepicker/ net::ERR_ABORTED 404

GET http://localhost:9000/static/appbuilder/datepicker/bootstrap-datepicker.css net::ERR_ABORTED 404
        
GET http://localhost:9000/static/appbuilder/select2/select2.css net::ERR_ABORTED 404
        
GET http://localhost:9000/static/appbuilder/select2/select2-bootstrap-theme.css net::ERR_ABORTED 404

These references were introduced by #24390.

The new references are:

GET http://localhost:9000/static/appbuilder/css/bootstrap-datepicker/bootstrap-datepicker3.min.css

GET http://localhost:9000/static/appbuilder/css/select2/select2.min.css

GET http://localhost:9000/static/appbuilder/css/select2/select2-bootstrap.min.css

Fixes #26267

Fixes #26072

TESTING INSTRUCTIONS

Follow the instructions in the original issue.

ADDITIONAL INFORMATION

• Has associated issue:
• Required feature flags:
• 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

[michael-s-molina]

The actual change is fixing these 4 lines. The rest is just HTML formatting.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (429e2a3) 66.99% compared to head (6ea1144) 66.99%.
Report is 38 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #26302      +/-   ##
==========================================
- Coverage   66.99%   66.99%   -0.01%     
==========================================
  Files        1945     1945              
  Lines       75949    75946       -3     
  Branches     8460     8460              
==========================================
- Hits        50885    50878       -7     
- Misses      22879    22883       +4     
  Partials     2185     2185              

Flag	Coverage Δ
mysql	78.07% <ø> (+0.01%)	⬆️
postgres	78.17% <ø> (-0.02%)	⬇️
python	78.31% <ø> (-0.02%)	⬇️
sqlite	76.83% <ø> (-0.02%)	⬇️

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