Fix incorrect API doc examples and copy-pasted descriptions

Replicates graphql/graphql-js@e35a025

Author: Cito

src/graphql/type/definition.py

@@ -2733,7 +2733,9 @@ def value_to_literal(self, value: Any) -> ConstValueNode | None:
         >>> rgb_type = GraphQLEnumType('RGB', {'RED': 0, 'GREEN': 1, 'BLUE': 2})
         >>> print_ast(rgb_type.value_to_literal('BLUE'))
         'BLUE'
-        >>> rgb_type.value_to_literal(3) is None
+        >>> rgb_type.value_to_literal(2) is None
+        True
+        >>> rgb_type.value_to_literal('PURPLE') is None
         True
         """
         if isinstance(value, str) and self.values.get(value):

src/graphql/utilities/type_info.py

@@ -548,7 +548,7 @@ def enter(self, node: Node) -> None:
             method(node)
 
     def leave(self, node: Node) -> None:
-        """Update this TypeInfo instance for a left AST node.
+        """Update this TypeInfo instance when leaving an AST node.
 
         :param node: AST node being left.
 

src/graphql/validation/rules/defer_stream_directive_on_valid_operations_rule.py

@@ -88,9 +88,9 @@ def can_be_skipped_via_include_directive(node: DirectiveNode) -> bool:
 class DeferStreamDirectiveOnValidOperationsRule(ASTValidationRule):
     """Defer and stream directives are used on valid operations
 
-    A GraphQL document is only valid if defer and stream directives are not used
-    in subscription operations, unless they can be disabled via their ``if``
-    argument or the selection can be skipped via ``@skip`` or ``@include``.
+    Subscription operations must not use unconditional ``@defer`` or ``@stream``.
+    Their ``if`` argument must be ``false`` or a variable, unless the selection or
+    an enclosing selection can be skipped via ``@skip`` or ``@include``.
 
     :param context: The validation context used while checking the document.