test: fix misspelled test identifiers

[wangjingshuiku]

Fix two spelling errors in test-only identifiers and descriptions:

• checkumFiles → checksumFiles in the checksum test suite description;
• secondRequst → secondRequest in the sandbox state test.

Assertions, fixtures, snapshots, and production behavior are unchanged. Deprecated compatibility identifiers with historical spelling are intentionally left intact.

Validation:

`npx prettier --check packages/snaps-utils/src/checksum.test.ts packages/snaps-sandbox/src/state.test.ts`

---

Note

Low Risk
Test-only identifier and describe-block renames with no production or behavioral impact.

Overview
This PR only renames misspelled test-only symbols so names match the real APIs and intent. No assertions, fixtures, or runtime behavior change.

In packages/snaps-sandbox/src/state.test.ts, the history update test renames secondRequst to secondRequest everywhere it is declared, stored in persistedHistoryAtom, and spread into updatedRequest.

In packages/snaps-utils/src/checksum.test.ts, the outer describe label is corrected from checkumFiles to checksumFiles, aligning the suite title with the imported function under test.

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