Add documentation examples for not-context-manager (#7051)

Co-authored-by: Vladyslav Krylasov <[email protected]>
Co-authored-by: Pierre Sassoulas <[email protected]>

Author: 3 people

doc/data/messages/n/not-context-manager/bad.py

@@ -0,0 +1,7 @@
+class MyContextManager:
+    def __enter__(self):
+        pass
+
+
+with MyContextManager() as c:  # [not-context-manager]
+    pass

doc/data/messages/n/not-context-manager/details.rst

@@ -1 +1,10 @@
-# This is a placeholder for correct code for this message.
+class MyContextManager:
+    def __enter__(self):
+        pass
+
+    def __exit__(self, *exc):
+        pass
+
+
+with MyContextManager() as c:
+    pass