Response::guardAgainstOutput(): add filename and line number

Co-authored-by: Lukas Bestle <lukas@getkirby.com>

src/Http/Response.php

@@ -188,10 +188,10 @@ public static function guardAgainstOutput(Closure $callback, ...$args): mixed
 	{
 		$before = headers_sent();
 		$result = $callback($args);
-		$after  = headers_sent();
+		$after  = headers_sent($file, $line);
 
 		if ($before === false && $after === true) {
-			throw new LogicException('Disallowed output from file $file:$line, possible accidental whitespace?');
+			throw new LogicException("Disallowed output from file $file:$line, possible accidental whitespace?");
 		}
 
 		return $result;