test: Fixes act errors in TimezoneSelector test

[michael-s-molina]

SUMMARY

This PR fixes 3 act errors in superset-frontend/src/components/TimezoneSelector/TimezoneSelector.test.tsx

TESTING INSTRUCTIONS

• Execute the component tests
• 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 #21377 (6fa7a62) into master (0601b2d) will increase coverage by 0.00%.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master   #21377   +/-   ##
=======================================
  Coverage   66.61%   66.61%           
=======================================
  Files        1791     1791           
  Lines       68538    68559   +21     
  Branches     7310     7319    +9     
=======================================
+ Hits        45655    45671   +16     
  Misses      21002    21002           
- Partials     1881     1886    +5     

Flag	Coverage Δ
javascript	52.80% <ø> (+0.01%)	⬆️

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

Impacted Files	Coverage Δ
...ard/components/DrillDetailPane/DrillDetailPane.tsx	81.01% <0.00%> (-1.75%)	⬇️
...rset-frontend/src/components/MetadataBar/index.tsx
...rontend/src/components/MetadataBar/MetadataBar.tsx	96.00% <0.00%> (ø)

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