Fix PHPStan Prometheus\Counter::incBy()label type

src/Prometheus/Counter.php

@@ -28,7 +28,7 @@ public function inc(array $labels = []): void
 
     /**
      * @param int|float $count e.g. 2
-     * @param string[] $labels e.g. ['status', 'opcode']
+     * @param array<int|string> $labels e.g. ['status', 'opcode']
      */
     public function incBy($count, array $labels = []): void
     {