Format code in common style in example of protocol implementation for class object

Author: e1turin

docs/spec/protocol.rst

@@ -502,12 +502,15 @@ For example::
   from typing import Any, Protocol
 
   class ProtoA(Protocol):
-      def meth(self, x: int) -> int: ...
+      def meth(self, x: int) -> int:
+          ...
   class ProtoB(Protocol):
-      def meth(self, obj: Any, x: int) -> int: ...
+      def meth(self, obj: Any, x: int) -> int:
+          ...
 
   class C:
-      def meth(self, x: int) -> int: ...
+      def meth(self, x: int) -> int:
+          ...
 
   a: ProtoA = C()  # OK
   b: ProtoB = C()  # Error: signatures don't match