Fix false-positives appearing when cache is in use

Author: David Robertson

src/mypy_zope/plugin.py

@@ -695,7 +695,7 @@ def _apply_interface(self, impl: TypeInfo, iface: TypeInfo) -> None:
         # there is a decorator for the class that will create a "type promotion",
         # but ensure this only gets applied a single time per interface.
         promote = Instance(iface, [])
-        if not any(ti._promote == promote for ti in impl.mro):
+        if not any(promote in ti._promote for ti in impl.mro):
             faketi = TypeInfo(SymbolTable(), iface.defn, iface.module_name)
             faketi._promote = [promote]
             impl.mro.append(faketi)