[TSan] Ensure test uses tagged pointer

This is a test-only failure. The test wrongly assumes that this gets us
a tagged pointer:
```
NSObject* num1 = @7;
assert(isTaggedPtr(num1));
```

However, on newer deployment targets that have “const data support” we
get a “normal” pointer to constant object.

Radar-Id: rdar://problem/83217293