fix(yarn): incorrect logic around caching of locked versions (#7330)

The issue is that the compatibility was only being set for the first `package.json` that was detected, due to how this if/else statement was constructed.

https://github.com/renovatebot/renovate/blob/1b99f4f0f7011f48b90250540c2b60cf2b1c9d20/lib/manager/npm/extract/locked-versions.ts#L16-L30

`isYarn1`, and the following logic, was only being executed if the lockfile was _not_ found in the cache.