Update npm dependencies to latest stable versions

[JoshLuedeman]

Summary

npm dependencies in this TypeScript GitHub Action need to be updated.

Current State

Package	Current	Notes
typescript	^4.8.4	Move to ^5.x
@actions/core	^1.10.0	Check latest
actions-toolkit	^6.0.1	Check latest
zod	^3.20.2	Check latest
nunjucks	^3.2.3	Check latest

Acceptance Criteria

• Run npm update to bring all deps to latest within declared ranges
• Update typescript constraint to ^5.x
• Run npm audit and resolve any CVEs
• Run npm test
• Rebuild dist with npm run build

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