fix: typos in code comments (#97137)
## Summary
- Fix "occurence" → "occurrence" in `test/lib/router-act.ts`
- Fix "wether" → "whether" in
`packages/next/src/server/stream-utils/encoded-tags.ts`
## Test plan
- [x] Changes are comment-only, no code logic affected
Attribution: This change was originally authored by @evandroreichert in
#90785.
Co-authored-by: Evandro <evandroreichert07@gmail.com>
