Fix type error (#12899)

Possible float in convertToBytes.
Assuming the original number is a float and it isn't accurate, could end up with a float.

includes/polling/applications/docker.inc.php

@@ -24,7 +24,7 @@ function convertToBytes(string $from): ?int
         return null;
     }
 
-    return $number * (1024 ** $exponent);
+    return (int) ($number * (1024 ** $exponent));
 }
 
 try {