Fixed #36051 -- Declared arity on aggregate functions.

Follow-up to 4a66a69239.

docs/ref/models/expressions.txt

@@ -516,6 +516,7 @@ generated. Here's a brief example::
         function = "SUM"
         template = "%(function)s(%(all_values)s%(expressions)s)"
         allow_distinct = False
+        arity = 1
 
         def __init__(self, expression, all_values=False, **extra):
             super().__init__(expression, all_values="ALL " if all_values else "", **extra)

docs/releases/5.2.txt

@@ -511,6 +511,10 @@ Miscellaneous
 * The minimum supported version of ``oracledb`` is increased from 1.3.2 to
   2.3.0.
 
+* Built-in aggregate functions accepting only one argument (``Avg``, ``Count``,
+  ``Max``, ``Min``, ``StdDev``, ``Sum``, and ``Variance``) now raise
+  :exc:`TypeError` when called with an incorrect number of arguments.
+
 .. _deprecated-features-5.2:
 
 Features deprecated in 5.2