cmd/go/internal/load: join incompatible and dirty build specifiers with .
Change "+incompatible+dirty" version to be "+incompatible.dirty" such
that it is SemVer spec compatible.
Fixes #71971
Change-Id: I714ffb3f1ad88c793656c3652367db34739a2144
Reviewed-on: https://go-review.googlesource.com/c/go/+/652955
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Sam Thanawalla <samthanawalla@google.com> Reviewed-by: Sean Liao <sean@liao.dev>
Auto-Submit: Sean Liao <sean@liao.dev> Reviewed-by: Michael Matloob <matloob@golang.org>