Fix MERCHANTABILITY typo in workers types header

[Hashim1999164]

Summary

• Corrects MERCHANTABLITY to MERCHANTABILITY in the generated Workers types license header.
• Updates the matching test expectation and committed generated snapshots.

Fixes #3940 (spelling reported in follow-up comments).

Test plan

• Confirm header spelling in types/src/index.ts
• bazel test //types:all if practical

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[Hashim1999164]

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