test: Fix act errors in SamplesPane test

[lyndsiWilliams]

SUMMARY

This PR fixes 8 act errors in superset-frontend/src/explore/components/DataTablesPane/test/SamplesPane.test.tsx

TESTING INSTRUCTIONS

• cd into superset-frontend/src/explore/components/DataTablesPane/test
• run npm run test superset-frontend/src/explore/components/DataTablesPane/test/SamplesPane.test.tsx
• Observe that there are no act errors in the console

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 #21406 (be108c0) into master (71459a6) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master   #21406   +/-   ##
=======================================
  Coverage   66.58%   66.58%           
=======================================
  Files        1791     1791           
  Lines       68559    68559           
  Branches     7319     7319           
=======================================
  Hits        45647    45647           
  Misses      21022    21022           
  Partials     1890     1890           

Flag	Coverage Δ
hive	52.97% <ø> (ø)
javascript	52.74% <ø> (ø)
mysql	80.83% <ø> (ø)
postgres	80.88% <ø> (ø)
presto	52.87% <ø> (ø)
python	81.36% <ø> (ø)
sqlite	79.43% <ø> (ø)
unit	50.83% <ø> (ø)

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