[monotouch-test] Fix bool encoding in tests on ARM64 on Mac Catalyst. (…

…xamarin#17695)

Fixes:

    [FAIL] TestTypeEncodings :   xamarin#14
        String lengths are both 1. Strings differ at index 0.
        Expected: "B"
        But was:  "c"
        -----------^

tests/monotouch-test/ObjCRuntime/RegistrarTest.cs

@@ -1455,6 +1455,8 @@ public void TestTypeEncodings ()
 			var sig = Runtime.GetNSObject<NSMethodSignature> (Messaging.IntPtr_objc_msgSend_IntPtr (cl.Handle, Selector.GetHandle ("methodSignatureForSelector:"), Selector.GetHandle ("foo::::::::::::::::")));
 #if MONOMAC
 			var boolEncoding = TrampolineTest.IsArm64CallingConvention ? "B" : "c";
+#elif __MACCATALYST__
+			var boolEncoding = "B";
 #else
 			var boolEncoding = (IntPtr.Size == 8 || TrampolineTest.IsArmv7k || TrampolineTest.IsArm64CallingConvention) ? "B" : "c";