issue 68890: add more minimal repro

src/test/ui/parser/issue-68890-2.rs

@@ -0,0 +1,3 @@
+type X = (?'a) +;
+//~^ ERROR `?` may only modify trait bounds, not lifetime bounds
+//~| ERROR expected trait bound, not lifetime bound

src/test/ui/parser/issue-68890-2.stderr

@@ -0,0 +1,14 @@
+error: `?` may only modify trait bounds, not lifetime bounds
+  --> $DIR/issue-68890-2.rs:1:11
+   |
+LL | type X = (?'a) +;
+   |           ^
+
+error: expected trait bound, not lifetime bound
+  --> $DIR/issue-68890-2.rs:1:11
+   |
+LL | type X = (?'a) +;
+   |           ^^^
+
+error: aborting due to 2 previous errors
+