runtime/pprof: TestVMInfo reworked to avoid test flakiness.

runtime/pprof: TestVMInfo reworked to avoid test flakiness.

Fixes #62352.

Change-Id: Ib137a5f39d4630c4737badfabe8e6740593ecbcf
Reviewed-on: https://go-review.googlesource.com/c/go/+/527276
Reviewed-by: Cherry Mui <cherryyz@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Bryan Mills <bcmills@google.com>
Run-TryBot: Bryan Mills <bcmills@google.com>