Type check is_isomorphic

Added a type check to .is_isomorphic to ensure that A is a quaternion algebra of the form (a,b)_K.

Author: S17A05

src/sage/algebras/quatalg/quaternion_algebra.py

@@ -1091,6 +1091,9 @@ def is_isomorphic(self, A) -> bool:
             sage: A == B
             False
         """
+        if not isinstance(A, QuaternionAlgebra_ab):
+            raise TypeError("A must be a quaternion algebra of the form (a,b)_K")
+
         if self.base_ring() != QQ or A.base_ring() != QQ:
             raise NotImplementedError("isomorphism check only implemented for rational quaternion algebras")