setup_rts.adb: update after a recent GPR2 API breaking change

Change-Id: Ic69fbdc960c3fd0d4066658c03f7dd619062cecc
TN: V830-027

Author: pmderodat

tools/gnatcov/setup_rts.adb

@@ -505,7 +505,7 @@ package body Setup_RTS is
       --  string for the Library_Support attribute.
 
       declare
-         Attr_Id : constant GPR2.Attribute_Id :=
+         Attr_Id : constant GPR2.Q_Attribute_Id :=
            GPR2.Project.Registry.Attribute.Library_Support;
          Attr    : constant GPR2.Project.Attribute.Object :=
            Prj.Configuration.Corresponding_View.Attribute (Attr_Id);