cmd/cgo/internal/testshared: skip in short mode and not on builders
We already skip testcarchive, testcshared, and testplugin in short
mode and not on builders. The shared build mode is not more
supported than the c-archive, c-shared, and plugin build modes. No
need to run it everywhere by default.
Updates #61025.
Change-Id: I6a06e04c1a1dc78f0f85456320d128bd67277915
Reviewed-on: https://go-review.googlesource.com/c/go/+/511696
Run-TryBot: Cherry Mui <cherryyz@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: Than McIntosh <thanm@google.com>