Clean up test suite console warnings

[chownces]

Description

Clean up the console warnings emitted since the migration out of enzyme testing library in https://github.com/source-academy/frontend/issues/2520.

Note:

• BackendSaga.ts tests are in https://github.com/source-academy/frontend/pull/2952
• Can't figure out the Ace editor issue yet though - filed a separate issue for it https://github.com/source-academy/frontend/issues/2962
• PersistenceSaga not yet done

Type of change

• [x] Code quality improvements

How to test

Checklist

• [x] I have tested this code

[coveralls]

Pull Request Test Coverage Report for Build 8911684941

Details

• 2 of 2 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 33.067%

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Totals
Change from base Build 8911671439:	0.0%
Covered Lines:	5299
Relevant Lines:	14893

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💛 - Coveralls