replace unreachable with error

Author: dylwil3

crates/ruff_python_parser/src/parser/expression.rs

@@ -1685,14 +1685,14 @@ impl<'src> Parser<'src> {
                         return;
                     }
                     tok => {
-                        // This should never happen because the list parsing will only
-                        // call this closure for the above token kinds which are the same
-                        // as in the FIRST set.
-                        unreachable!(
-                            "{}: unexpected token `{tok:?}` at {:?}",
-                            string_kind,
-                            parser.current_token_range()
+                        parser.add_error(
+                            ParseErrorType::OtherError(format!(
+                                "{string_kind}: unexpected token `{tok:?}`"
+                            )),
+                            parser.current_token_range(),
                         );
+                        parser.bump_any();
+                        return;
                     }
                 };
                 elements.push(element);