Copy name when cloning FKs recurses to partitions

We were passing a string owned by a syscache entry, which was released
before recursing.  Fix by pstrdup'ing the string.

Per buildfarm member prion.

Author: alvherre

src/backend/commands/tablecmds.c

@@ -8619,7 +8619,7 @@ CloneFkReferencing(List **wqueue, Relation parentRel, Relation partRel)
 									 "fkey",
 									 RelationGetNamespace(partRel), NIL);
 		else
-			fkconstraint->conname = NameStr(constrForm->conname);
+			fkconstraint->conname = pstrdup(NameStr(constrForm->conname));
 		fkconstraint->fk_upd_action = constrForm->confupdtype;
 		fkconstraint->fk_del_action = constrForm->confdeltype;
 		fkconstraint->deferrable = constrForm->condeferrable;