chore: chart deletion test for slice user

[AAfghahi]

SUMMARY

Some users were experiencing an foreign key error when trying to delete a chart or a dashboard for slice_user and sqlatable_user. Just adding some test to makes sure those possibilities are taken into account.

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 #22703 (134c613) into master (af34e45) will decrease coverage by 13.30%.
The diff coverage is 100.00%.

@@             Coverage Diff             @@
##           master   #22703       +/-   ##
===========================================
- Coverage   67.02%   53.73%   -13.30%     
===========================================
  Files        1859     1866        +7     
  Lines       71036    75039     +4003     
  Branches     7766     7766               
===========================================
- Hits        47612    40320     -7292     
- Misses      21401    32697    +11296     
+ Partials     2023     2022        -1     

Flag	Coverage Δ
hive	53.37% <100.00%> (+0.89%)	⬆️
javascript	53.85% <ø> (-0.02%)	⬇️
mysql	?
postgres	?
presto	52.37% <100.00%> (+<0.01%)	⬆️
python	53.60% <100.00%> (-27.75%)	⬇️
sqlite	?
unit	?

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

Impacted Files	Coverage Δ
superset/charts/commands/delete.py	47.50% <100.00%> (-44.81%)	⬇️
superset/models/slice.py	58.53% <100.00%> (-27.32%)	⬇️
superset/utils/dashboard_import_export.py	0.00% <0.00%> (-100.00%)	⬇️
superset/extensions/metastore_cache.py	0.00% <0.00%> (-98.08%)	⬇️
superset/tags/core.py	4.54% <0.00%> (-95.46%)	⬇️
superset/key_value/commands/update.py	0.00% <0.00%> (-90.91%)	⬇️
superset/key_value/commands/delete.py	0.00% <0.00%> (-87.88%)	⬇️
superset/key_value/commands/delete_expired.py	0.00% <0.00%> (-84.00%)	⬇️
...set/advanced_data_type/plugins/internet_address.py	16.32% <0.00%> (-79.60%)	⬇️
superset/utils/pandas_postprocessing/boxplot.py	20.51% <0.00%> (-79.49%)	⬇️
... and 348 more

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[rusackas]

Closing this, but pinging @eschutho and @yousoph in case you want to revisit it.