cmd/pprof: update vendored github.com/google/pprof

Pull in the latest published version of github.com/google/pprof
that is available at this time in the Go 1.18 development cycle.

Done with:

	go get -d github.com/google/pprof@latest
	go mod tidy
	go mod vendor

For #36905.

Change-Id: Ib25aa38365ec70a0bed2a8a6527e5823ab9f9ded
Reviewed-on: https://go-review.googlesource.com/c/go/+/348410


Trust: Dmitri Shuralyov <dmitshur@golang.org>
Run-TryBot: Dmitri Shuralyov <dmitshur@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Michael Pratt <mpratt@google.com>