runtime: skip TestStackSwitchCallback on ios

getcontext is unsupported on ios, returning ENOTSUP.

Fixes #62700.

Change-Id: Icc6c45fbd574886766d5289e2fbdbd62981d77eb
Reviewed-on: https://go-review.googlesource.com/c/go/+/529216
Run-TryBot: Michael Pratt <[email protected]>
Reviewed-by: Bryan Mills <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: Than McIntosh <[email protected]>
Reviewed-by: Cherry Mui <[email protected]>
Auto-Submit: Michael Pratt <[email protected]>

Author: prattmic

src/runtime/crash_cgo_test.go

@@ -873,7 +873,7 @@ func TestEnsureBindM(t *testing.T) {
 func TestStackSwitchCallback(t *testing.T) {
 	t.Parallel()
 	switch runtime.GOOS {
-	case "windows", "plan9", "android", "openbsd": // no getcontext
+	case "windows", "plan9", "android", "ios", "openbsd": // no getcontext
 		t.Skipf("skipping test on %s", runtime.GOOS)
 	}
 	got := runTestProg(t, "testprogcgo", "StackSwitchCallback")