[UBSan] Relax test expectations in Misc/objc-cast.m test

The test checks that an array of Obj-C literal integers (e.g. `@1`) gets a UBSan
warning when cast to an NSString, however the actual concrete Obj-C class of
literal integers doesn't always need to be __NSCFNumber. Let's relax the test
expectations to allow NSConstantIntegerNumber. Which exact subclass of NSNumber
is used is not actually important for the test (the test is just checking that
the invalid cast warning is thrown).