Rollup merge of #69014 - dwrensha:fix-68890, r=Centril

change an instance of span_bug() to struct_span_err() to avoid ICE

After #67148, the `span_bug()` in `parse_ty_tuple_or_parens()` is reachable because `parse_paren_comma_seq()` can return an `Ok()` even in cases where it encounters an error.
This pull request prevents an ICE in such cases by replacing the `span_bug()` with `struct_span_error()`.

Fixes #68890.

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

@@ -0,0 +1,4 @@
+enum e{A((?'a a+?+l))}
+//~^ ERROR `?` may only modify trait bounds, not lifetime bounds
+//~| ERROR expected one of `)`, `+`, or `,`
+//~| ERROR expected trait bound, not lifetime bound

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

@@ -0,0 +1,20 @@
+error: `?` may only modify trait bounds, not lifetime bounds
+  --> $DIR/issue-68890.rs:1:11
+   |
+LL | enum e{A((?'a a+?+l))}
+   |           ^
+
+error: expected one of `)`, `+`, or `,`, found `a`
+  --> $DIR/issue-68890.rs:1:15
+   |
+LL | enum e{A((?'a a+?+l))}
+   |               ^ expected one of `)`, `+`, or `,`
+
+error: expected trait bound, not lifetime bound
+  --> $DIR/issue-68890.rs:1:11
+   |
+LL | enum e{A((?'a a+?+l))}
+   |           ^^^
+
+error: aborting due to 3 previous errors
+