fix: adjust to upcoming Hecke changes (#4730)

(cherry picked from commit a7a5a93)
Signed-off-by: Aaruni Kaushik <aaruni@edufor.me>

Author: thofma

experimental/GaloisGrp/src/Subfields.jl

@@ -5,6 +5,10 @@ using Oscar.GaloisGrp
 import Oscar.GaloisGrp: POSet, POSetElem, GaloisCtx, find_prime,
                         primitive_by_shape, bound_to_precision
 
+if isdefined(Oscar, :subfield)
+  import Oscar: subfield
+end
+
 
 function embedding_hom(k, K)
   return MapFromFunc(k, K, K)