internal/lsp/cache: use the right snapshot in ModUpgrade
internal/lsp/cache: use the right snapshot in ModUpgrade

Cache computations need to use the passed in snapshot.

Fixes golang/go#41056.

Change-Id: I09501f3fc6abccedcf33482c9ee4d58146fbe716
Reviewed-on: https://go-review.googlesource.com/c/tools/+/252437
Run-TryBot: Heschi Kreinick <e89ab2b172855aa0ad01c40c4d8a3535a61ac68a@google.com>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Rebecca Stambler <d7cf11e5f299d88ea8348366a9fc4f7c335c3afa@golang.org>

golang/tools,golang/tools,golang/tools,golang/tools,golang/tools