runtime: set userForced while holding gcsema

runtime: set userForced while holding gcsema

Fixes #52515

Change-Id: If10068a97733daf61aba72da5ed3935db8eed8b9
Reviewed-on: https://go-review.googlesource.com/c/go/+/401776
Reviewed-by: hopehook <hopehook@golangcn.org>
Run-TryBot: hopehook <hopehook@golangcn.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Auto-Submit: Jenny Rakoczy <jenny@golang.org>
Run-TryBot: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Jenny Rakoczy <jenny@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>