runtime/pprof: skip flaky test TestProfilerStackDepth/heap for now

The test has been causing a lot of flakes on the builders. Skip it while
I'm debugging it.

For #74029

Change-Id: I6a6a696450c23f65bc310a2d0ab61b22dba88f00
Reviewed-on: https://go-review.googlesource.com/c/go/+/712060
TryBot-Bypass: Michael Matloob <matloob@google.com>
Reviewed-by: Michael Matloob <matloob@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>

Author: matloob

src/runtime/pprof/pprof_test.go

@@ -2549,6 +2549,9 @@ func TestProfilerStackDepth(t *testing.T) {
 
 	for _, test := range tests {
 		t.Run(test.profiler, func(t *testing.T) {
+			if test.profiler == "heap" {
+				testenv.SkipFlaky(t, 74029)
+			}
 			var buf bytes.Buffer
 			if err := Lookup(test.profiler).WriteTo(&buf, 0); err != nil {
 				t.Fatalf("failed to write heap profile: %v", err)