Fix bad decoding for x-matched-path header (#78677)
This is a follow-up to https://github.com/vercel/next.js/pull/78326
which reverts the change that interferes with the added middleware
rewrite test while also ensuring the encoding test from the
`vercel/vercel` repo is still passing as expected. The issue with the
encoding seems to be from the `x-matched-path` value being incorrectly
decoded when using non-utf8 characters so this fixes the encoding.
Fixes:
https://github.com/vercel/next.js/actions/runs/14717733032/attempts/2
<details>
<summary>test runs with patch</summary>
</details>
