add regression test for #74713

Author: TaKO8Ki

src/test/ui/const-generics/generic_const_exprs/issue-74713.rs

@@ -0,0 +1,8 @@
+fn bug<'a>()
+where
+    [(); { //~ ERROR mismatched types
+        let _: &'a (); //~ ERROR a non-static lifetime is not allowed in a `const`
+    }]:
+{}
+
+fn main() {}

src/test/ui/const-generics/generic_const_exprs/issue-74713.stderr

@@ -0,0 +1,22 @@
+error[E0658]: a non-static lifetime is not allowed in a `const`
+  --> $DIR/issue-74713.rs:4:17
+   |
+LL |         let _: &'a ();
+   |                 ^^
+   |
+   = note: see issue #76560 <https://github.com/rust-lang/rust/issues/76560> for more information
+   = help: add `#![feature(generic_const_exprs)]` to the crate attributes to enable
+
+error[E0308]: mismatched types
+  --> $DIR/issue-74713.rs:3:10
+   |
+LL |       [(); {
+   |  __________^
+LL | |         let _: &'a ();
+LL | |     }]:
+   | |_____^ expected `usize`, found `()`
+
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0308, E0658.
+For more information about an error, try `rustc --explain E0308`.