Fix ssgCacheKey in minimal mode (#59181)
This ensures we use the correct `srcPathname` in minimal mode so that we
can normalize the URL and generate the correct `ssgCacheKey` which is
used for request caching/de-duping.
We aren't able to add a reliable test case for this as it is a race
condition within a second of a previous request although this was
verified against a stress test repro here
https://overlapping-segments-h1455lwvk-vtest314-ijjk-testing.vercel.app/repro/tutorials/demo
This behavior seems to have regressed in
https://github.com/vercel/next.js/pull/45716
Closes NEXT-1777
