fix: datasourcedao datasource not found error

[pkdotson]

SUMMARY

This pr is a possible fix for potential error of having the wrong type for the datasource type and causing a validation error being thrown.

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 #20725 (2fa82a4) into master (84d4302) will decrease coverage by 0.19%.
The diff coverage is 100.00%.

❗ Current head 2fa82a4 differs from pull request most recent head e939697. Consider uploading reports for the commit e939697 to get more accurate results

@@            Coverage Diff             @@
##           master   #20725      +/-   ##
==========================================
- Coverage   66.30%   66.11%   -0.20%     
==========================================
  Files        1756     1756              
  Lines       66734    66737       +3     
  Branches     7049     7049              
==========================================
- Hits        44248    44121     -127     
- Misses      20689    20819     +130     
  Partials     1797     1797              

Flag	Coverage Δ
hive	?
mysql	81.04% <100.00%> (+<0.01%)	⬆️
postgres	81.11% <100.00%> (+<0.01%)	⬆️
presto	?
python	81.16% <100.00%> (-0.40%)	⬇️
sqlite	?
unit	?

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

Impacted Files	Coverage Δ
superset/views/core.py	75.07% <ø> (-0.61%)	⬇️
superset/datasource/dao.py	100.00% <100.00%> (ø)
superset/db_engines/hive.py	0.00% <0.00%> (-85.19%)	⬇️
superset/db_engine_specs/hive.py	70.22% <0.00%> (-15.65%)	⬇️
superset/db_engine_specs/sqlite.py	91.89% <0.00%> (-5.41%)	⬇️
superset/db_engine_specs/presto.py	83.64% <0.00%> (-5.39%)	⬇️
superset/utils/celery.py	86.20% <0.00%> (-3.45%)	⬇️
superset/connectors/sqla/utils.py	86.36% <0.00%> (-2.28%)	⬇️
superset/initialization/__init__.py	89.93% <0.00%> (-1.74%)	⬇️
superset/result_set.py	96.24% <0.00%> (-1.51%)	⬇️
... and 5 more

[eschutho]

@hughhhh @pkdotson I see that this endpoint is deprecated but why are we only using table here?