fix(hashing): include default files in fallback (#7106)
### Description
Stacked on top of https://github.com/vercel/turbo/pull/7105 (review
first)
Fallback git hashing fixes - include `package.json` and `turbo.json` by
default if a manual input array has been provided and we're using
fallback (non git) hashing.
This is done to mimic the standard behavior (non fallback):
https://github.com/vercel/turbo/blob/main/crates/turborepo-scm/src/package_deps.rs#L160-L171
Closes TURBO-2157
