gh-37360: Fix doctest for multiplication_by_m

    
The current doctest can create a singular curve, for example with
`random-seed=129979402993014347526756638208394445987`.
    
URL: #37360
Reported by: Sebastian A. Spindler
Reviewer(s): grhkm21

src/sage/schemes/elliptic_curves/ell_generic.py

@@ -2449,7 +2449,7 @@ def multiplication_by_m(self, m, x_only=False):
 
             sage: p = 7
             sage: K.<a> = GF(p^2)
-            sage: E = EllipticCurve(K, [K.random_element(), K.random_element()])
+            sage: E = EllipticCurve(j=K.random_element())
             sage: E.multiplication_by_m(p * 2)[0] == E.multiplication_by_m(p * 2, x_only=True)
             True
         """