gh-37165: use Parent in quadratic number fields

    
as another little step towards getting rid of `ParentWithBase`

### 📝 Checklist

- [x] The title is concise, informative, and self-explanatory.
- [x] The description explains in detail what this PR is about.
    
URL: #37165
Reported by: Frédéric Chapoton
Reviewer(s): Marc Mezzarobba

src/sage/rings/number_field/number_field_element_quadratic.pyx

@@ -49,9 +49,7 @@ from sage.libs.ntl.ntl_ZZ cimport ntl_ZZ
 from sage.libs.ntl.ntl_ZZX cimport ntl_ZZX
 from sage.libs.mpfi cimport *
 
-
 from sage.structure.parent cimport Parent
-from sage.structure.parent_base cimport ParentWithBase
 from sage.structure.element cimport Element
 from sage.structure.richcmp cimport rich_to_bool_sgn
 
@@ -611,7 +609,7 @@ cdef class NumberFieldElement_quadratic(NumberFieldElement_absolute):
 
         mpz_clear(tmp_mpz)
 
-        x._parent = <ParentWithBase>new_parent
+        x._parent = <Parent>new_parent
         x._fld_numerator, x._fld_denominator = new_parent.polynomial_ntl()
         x._denominator = elt_den
         cdef ZZX_c result