Fix use of inaccessible member in pr85503.C [PR95716]

The recent PR41437 fix exposed a latent use of an inaccessible member in
the below testcase.

gcc/testsuite/ChangeLog:

	PR testsuite/95716
	* g++.dg/ext/pr85503.C: Give ai::cv public access.

gcc/testsuite/g++.dg/ext/pr85503.C

@@ -138,6 +138,7 @@ struct ad< ai< cr, ag, ah, cu, ct, cw > > {
 };
 template < typename, int ag, int ah, int, int, int >
 class ai : public af< ai< double, ag, ah > > {
+public:
   typedef ai cv;
 };
 template < typename bk, typename ce, typename cf >