cmd/go/testdata/script: skip vet_cache in short mode

vet_cache uses a clean cache

Change-Id: I68e9f32e60ad228785e9bf28f1c3a42e6a6a6964
Reviewed-on: https://go-review.googlesource.com/c/go/+/726961
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Michael Matloob <matloob@golang.org>
Reviewed-by: Alan Donovan <adonovan@google.com>
Reviewed-by: Michael Matloob <matloob@google.com>

Author: matloob

src/cmd/go/testdata/script/vet_cache.txt

@@ -1,6 +1,8 @@
 # Test that go vet's caching of vet tool actions replays
 # the recorded stderr output even after a cache hit.
 
+[short] skip 'uses a fresh build cache'
+
 # Set up fresh GOCACHE.
 env GOCACHE=$WORK/gocache