Add test for issue 102986

Author: WaffleLapkin

src/test/rustdoc-ui/issue-102986.rs

@@ -0,0 +1,4 @@
+struct Struct {
+    y: (typeof("hey"),),
+    //~^ `typeof` is a reserved keyword but unimplemented
+}

src/test/rustdoc-ui/issue-102986.stderr

@@ -0,0 +1,14 @@
+error[E0516]: `typeof` is a reserved keyword but unimplemented
+  --> $DIR/issue-102986.rs:2:9
+   |
+LL |     y: (typeof("hey"),),
+   |         ^^^^^^^^^^^^^ reserved keyword
+   |
+help: consider replacing `typeof(...)` with an actual type
+   |
+LL |     y: (&'static str,),
+   |         ~~~~~~~~~~~~
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0516`.