It is inconsistent to only compute IsIntermediateTestVariant for
workspace packages, and could be a source of bugs. Always compute it.

Change-Id: I16f40fe44a1145a74ef77fee4b7fd813abe603cb
Reviewed-on: https://go-review.googlesource.com/c/tools/+/340732
Reviewed-by: Alan Donovan <[email protected]>
gopls-CI: kokoro <[email protected]>
Run-TryBot: Robert Findley <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>