Raise error on every patch context manager

On pytest-dev#165, a change was
added to raise an Exception when trying to use `mocker.patch.object` as
a context manager, as its behavior is not supported in the plugin.
However, the context managers for the remaining patch options (dict,
multiple, and normal patch) still work as usual.

With this change, we check if we are in a context manager when starting
the patch, so all the methods will raise the exception if corresponds

src/pytest_mock/plugin.py

@@ -147,21 +147,17 @@ def _start_patch(self, mock_func, *args, **kwargs):
             module, registering the patch to stop it later and returns the
             mock object resulting from the mock call.
             """
+            self._enforce_no_with_context(inspect.stack())
             p = mock_func(*args, **kwargs)
             mocked = p.start()
             self._patches.append(p)
             if hasattr(mocked, "reset_mock"):
                 self._mocks.append(mocked)
             return mocked
 
-        def object(self, *args, **kwargs):
-            """API to mock.patch.object"""
-            self._enforce_no_with_context(inspect.stack())
-            return self._start_patch(self.mock_module.patch.object, *args, **kwargs)
-
         def _enforce_no_with_context(self, stack):
             """raises a ValueError if mocker is used in a with context"""
-            caller = stack[1]
+            caller = stack[2]
             frame = caller[0]
             info = inspect.getframeinfo(frame)
             code_context = " ".join(info.code_context).strip()
@@ -172,6 +168,10 @@ def _enforce_no_with_context(self, stack):
                     "https://github.com/pytest-dev/pytest-mock#note-about-usage-as-context-manager"
                 )
 
+        def object(self, *args, **kwargs):
+            """API to mock.patch.object"""
+            return self._start_patch(self.mock_module.patch.object, *args, **kwargs)
+
         def multiple(self, *args, **kwargs):
             """API to mock.patch.multiple"""
             return self._start_patch(self.mock_module.patch.multiple, *args, **kwargs)