Fix incorrect DSA attribute description (#13053)

Fix incorrect `key_size` attribute description (the bit length of the prime modulus).
Fixes issue #13052.

Author: upiter

docs/hazmat/primitives/asymmetric/dsa.rst

@@ -277,7 +277,7 @@ Key interfaces
 
         :type: int
 
-        The bit length of :attr:`~DSAParameterNumbers.q`.
+        The bit length of :attr:`~DSAParameterNumbers.p`.
 
     .. method:: sign(data, algorithm)
 
@@ -347,7 +347,7 @@ Key interfaces
 
         :type: int
 
-        The bit length of :attr:`~DSAParameterNumbers.q`.
+        The bit length of :attr:`~DSAParameterNumbers.p`.
 
     .. method:: parameters()