Fix typo in docs/deployment/index.md.

[wojcikstefan]

Summary

While reading https://uvicorn.dev/deployment/#built-in, I noticed a typo saying "processeses" instead of "processes".

Checklist

• I understand that this PR may be closed in case there was no previous discussion. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
  • Doesn't apply here :)
• I've updated the documentation accordingly.
  • This updates documentation only :)

[codspeed-hq]

Merging this PR will not alter performance

✅ 24 untouched benchmarks

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_{Comparing wojcikstefan:fix-typo-in-index (4326ccc) with main (ad5ff87)}

[Kludex]

Thanks!