Move regression test from compile-fail/ to ui/ test directory.

Author: pnkfelix

src/test/compile-fail/nll/issue-50716.rs renamed to src/test/ui/nll/issue-50716.rs

@@ -0,0 +1,8 @@
+error: free region `'a` does not outlive free region `'static`
+  --> $DIR/issue-50716.rs:25:14
+   |
+LL |     let _x = *s; //~ ERROR free region `'a` does not outlive free region `'static`
+   |              ^^
+
+error: aborting due to previous error
+