runtime: skip TestGdbBacktrace flakes matching a known GDB internal error

runtime: skip TestGdbBacktrace flakes matching a known GDB internal error

TestGdbBacktrace occasionally fails due to a GDB internal error.
We have observed the error on various linux builders since at least
October 2020, and it has been reported upstream at least twice.¹²

Since the bug is external to the Go project and does not appear to be
fixed upstream, this failure mode can only add noise.

¹https://sourceware.org/bugzilla/show_bug.cgi?id=24628
²https://sourceware.org/bugzilla/show_bug.cgi?id=28551

Fixes #43068

Change-Id: I6c92006a5d730f1c4df54b0307f080b3d643cc6b
Reviewed-on: https://go-review.googlesource.com/c/go/+/384234
Trust: Bryan Mills <bcmills@google.com>
Run-TryBot: Bryan Mills <bcmills@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>