runtime: add one extra lock ranking partial edge
This adds an assistQueue -> mheapSpecial edge, which can happen via
gcFlushBgCredit [gets assistQueue lock] -> ready() -> ... ->
allocm() -> newobject -> .. mProf_Malloc() ->
setprofilebucket() [gets mheap special lock]
From https://build.golang.org/log/
6f8f253f6c3a747de411cfdf78c27980146618be
Change-Id: Icdfba41b49aa704e8f6f20d25271f938afaf52ac
Reviewed-on: https://go-review.googlesource.com/c/go/+/231463
Run-TryBot: Dan Scales <danscales@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>