parser: change warn to error, for const names with upper letter (fix #18838) (#18840)

Author: yuyi98

vlib/v/checker/tests/const_field_name_snake_case.out

@@ -1,4 +1,4 @@
-vlib/v/checker/tests/const_field_name_snake_case.vv:2:2: warning: const names cannot contain uppercase letters, use snake_case instead
+vlib/v/checker/tests/const_field_name_snake_case.vv:2:2: error: const names cannot contain uppercase letters, use snake_case instead
     1 | const (
     2 |     Red = 1
       |     ~~~

vlib/v/parser/parser.v

@@ -3689,8 +3689,8 @@ fn (mut p Parser) const_decl() ast.ConstDecl {
 		pos := p.tok.pos()
 		name := p.check_name()
 		end_comments << p.eat_comments()
-		if util.contains_capital(name) {
-			p.warn_with_pos('const names cannot contain uppercase letters, use snake_case instead',
+		if !p.pref.translated && !p.is_translated && util.contains_capital(name) {
+			p.error_with_pos('const names cannot contain uppercase letters, use snake_case instead',
 				pos)
 		}
 		full_name := p.prepend_mod(name)