Pass all packages to go test, even if they don't have test files,
so that go test can still run vet.
I just got burned by a vet error in a package without a test
showing up when I added an (unrelated) test.
There are not enough packages without tests to be worth
the "savings" of not letting the go command vet those packages.
For #60463.
Change-Id: Ib9258655151144dce6a51deeae73d651aa46cb2c
Reviewed-on: https://go-review.googlesource.com/c/go/+/630015
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org> Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>