fix: docs for dynamic routing in next 15 (#71531)
### What?
Fixes the `params` prop in
https://nextjs.org/docs/canary/app/building-your-application/routing/dynamic-routes
Also fixes a typo: `synchronoulsy` -> `synchronously`
### Why?
There is a breaking change in `next@15.0.0-rc.1`:
https://nextjs.org/blog/next-15-rc2#async-request-apis-breaking-change
Although the api docs have been updated, these have not been.
### How?
updates the docs. (relevant) build and lint passes locally. ran the
prettier fix.
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Co-authored-by: JJ Kasper <jj@jjsweb.site>
