add a test for rust-lang#105709

replace build with check

Co-authored-by: Michael Goulet <michael@errs.io>

use appropriate test name

tests/ui/const-generics/generic_const_exprs/inline-const-in-const-generic-defaults.rs

@@ -0,0 +1,9 @@
+// check-pass
+
+#![feature(generic_const_exprs)]
+#![feature(inline_const)]
+#![allow(incomplete_features)]
+
+pub struct ConstDefaultUnstable<const N: usize = { const { 3 } }>;
+
+pub fn main() {}