c++: Add missing verify_type_context call [PR97904]

When adding the verify_type_context target hook, I'd missed
a site that needs to check an array element type.

gcc/cp/
	PR c++/97904
	* pt.c (tsubst): Use verify_type_context to check the type
	of an array element.

gcc/testsuite/
	PR c++/97904
	* g++.dg/ext/sve-sizeless-1.C: Add more template tests.
	* g++.dg/ext/sve-sizeless-2.C: Likewise.