fix: flash message on database data upload forms

[dpgaspar]

SUMMARY

Improve flash message on database data upload forms

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

TESTING INSTRUCTIONS

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

[codecov]

Codecov Report

Merging #21761 (9a22290) into master (d1a6f0e) will decrease coverage by 0.02%.
The diff coverage is 9.09%.

@@            Coverage Diff             @@
##           master   #21761      +/-   ##
==========================================
- Coverage   66.85%   66.83%   -0.03%     
==========================================
  Files        1800     1800              
  Lines       68957    68957              
  Branches     7335     7335              
==========================================
- Hits        46098    46084      -14     
- Misses      20966    20980      +14     
  Partials     1893     1893              

Flag	Coverage Δ
hive	52.93% <9.09%> (ø)
mysql	?
postgres	78.31% <9.09%> (ø)
presto	52.83% <9.09%> (ø)
python	81.41% <9.09%> (-0.05%)	⬇️
sqlite	76.80% <9.09%> (ø)
unit	51.05% <9.09%> (ø)

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

Impacted Files	Coverage Δ
superset/views/database/views.py	31.36% <9.09%> (ø)
superset/common/utils/dataframe_utils.py	90.47% <0.00%> (-4.77%)	⬇️
superset/db_engine_specs/mysql.py	94.04% <0.00%> (-4.77%)	⬇️
superset/models/core.py	89.41% <0.00%> (-0.71%)	⬇️
superset/views/core.py	75.60% <0.00%> (-0.46%)	⬇️

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more