test: Fix act errors in DndMetricSelect test

[lyndsiWilliams]

SUMMARY

This PR fixes 46 act errors in superset-frontend/src/explore/components/controls/DndColumnSelectControl/DndMetricSelect.test.tsx

TESTING INSTRUCTIONS

• cd into superset-frontend
• run npm run test superset-frontend/src/explore/components/controls/DndColumnSelectControl/DndMetricSelect.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 #22048 (e901ca8) into master (aa48cae) will not change coverage.
The diff coverage is n/a.

❗ Current head e901ca8 differs from pull request most recent head 1c8c488. Consider uploading reports for the commit 1c8c488 to get more accurate results

@@           Coverage Diff           @@
##           master   #22048   +/-   ##
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  Coverage   67.07%   67.07%           
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  Files        1815     1815           
  Lines       69575    69575           
  Branches     7486     7486           
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  Hits        46665    46665           
  Misses      20974    20974           
  Partials     1936     1936           

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javascript	53.57% <ø> (ø)

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[michael-s-molina]

LGTM