[release-branch.go1.12] runtime: skip broken TestLldbPython

It's broken on our builders (once we enabled dev mode on our Macs,
see CL 170339)

Updates #31188

Change-Id: Iceea65dc79576057b401a461bfe39254fed1f7ed
Reviewed-on: https://go-review.googlesource.com/c/go/+/170281Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
(cherry picked from commit 46c3e217)
Reviewed-on: https://go-review.googlesource.com/c/go/+/170798
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

src/runtime/runtime-lldb_test.go

@@ -139,6 +139,7 @@ func TestLldbPython(t *testing.T) {
 	if final := os.Getenv("GOROOT_FINAL"); final != "" && runtime.GOROOT() != final {
 		t.Skip("gdb test can fail with GOROOT_FINAL pending")
 	}
+	testenv.SkipFlaky(t, 31188)
 
 	checkLldbPython(t)