v.scanner: fix error messages with unexpected token `?` (#11428)

vlib/v/parser/tests/unexpected_token.out

@@ -0,0 +1,5 @@
+vlib/v/parser/tests/unexpected_token.vv:2:10: error: unexpected token `?`
+    1 | fn main() {
+    2 |     println(?)
+      |             ^
+    3 | }

vlib/v/parser/tests/unexpected_token.vv

@@ -0,0 +1,3 @@
+fn main() {
+	println(?)
+}

vlib/v/scanner/scanner.v

@@ -771,7 +771,7 @@ fn (mut s Scanner) text_scan() token.Token {
 				return s.new_token(.mod, '', 1)
 			}
 			`?` {
-				return s.new_token(.question, '', 1)
+				return s.new_token(.question, '?', 1)
 			}
 			scanner.single_quote, scanner.double_quote {
 				start_line := s.line_nr