docs(spanner): fix Instance.update() docstrings (#10106)

Author: Gurov Ilya

spanner/google/cloud/spanner_v1/instance.py

@@ -262,13 +262,13 @@ def update(self):
 
         .. note::
 
-           Updates the ``display_name`` and ``node_count``. To change those
-           values before updating, set them via
+            Updates the ``display_name`` and ``node_count``. To change those
+            values before updating, set them via
 
-           .. code:: python
+            .. code:: python
 
-              instance.display_name = 'New display name'
-              instance.node_count = 5
+                instance.display_name = 'New display name'
+                instance.node_count = 5
 
             before calling :meth:`update`.