chore: rename 'tables' to 'datasets' in error message

[mistercrunch]

see title

[codecov]

Codecov Report

Merging #15078 (7f39569) into master (834bb94) will decrease coverage by 0.07%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master   #15078      +/-   ##
==========================================
- Coverage   77.80%   77.73%   -0.08%     
==========================================
  Files         967      967              
  Lines       49668    49668              
  Branches     6326     6326              
==========================================
- Hits        38646    38607      -39     
- Misses      10821    10860      +39     
  Partials      201      201              

Flag	Coverage Δ
hive	81.44% <100.00%> (ø)
mysql	81.70% <100.00%> (ø)
postgres	81.73% <100.00%> (ø)
presto	?
python	82.10% <100.00%> (-0.15%)	⬇️
sqlite	81.35% <100.00%> (ø)

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

Impacted Files	Coverage Δ
superset/databases/commands/exceptions.py	94.00% <100.00%> (ø)
superset/db_engine_specs/presto.py	84.42% <0.00%> (-5.48%)	⬇️
superset/connectors/sqla/models.py	88.38% <0.00%> (-1.43%)	⬇️
superset/models/core.py	89.76% <0.00%> (-0.27%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 834bb94...7f39569. Read the comment docs.

[rusackas]

LGTM!