os/exec: skip TestContextCancel on netbsd/arm64

For #42061

Change-Id: I3b4c774ad9e375d4bfef1cfb4336c35ed30a6430
Reviewed-on: https://go-review.googlesource.com/c/go/+/372795
Trust: Bryan Mills <bcmills@google.com>
Run-TryBot: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

Author: Bryan C. Mills

src/os/exec/exec_test.go

@@ -954,6 +954,10 @@ func TestContext(t *testing.T) {
 }
 
 func TestContextCancel(t *testing.T) {
+	if runtime.GOOS == "netbsd" && runtime.GOARCH == "arm64" {
+		testenv.SkipFlaky(t, 42061)
+	}
+
 	// To reduce noise in the final goroutine dump,
 	// let other parallel tests complete if possible.
 	t.Parallel()