cmd/go: pass --no-decorate when listing git tags for a commit

cmd/go: pass --no-decorate when listing git tags for a commit

This avoids a parse error when the user's global .gitconfig sets
log.decorate to true.

Fixes #51312.

Change-Id: Ic47b0f604c0c3a404ec50d6e09f4e138045ac2f2
Reviewed-on: https://go-review.googlesource.com/c/go/+/387835
Run-TryBot: Bryan Mills <bcmills@google.com>
Auto-Submit: Bryan Mills <bcmills@google.com>
Reviewed-by: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>