Phpstan level 3

Author: casperbakker

src/Types/TypeCode11.php

@@ -106,6 +106,6 @@ private function getCheckDigitK(string $code): string
         }
         $check %= 11;
 
-        return $check;
+        return (string)$check;
     }
 }

src/Types/TypeCode32.php

@@ -109,6 +109,6 @@ protected function checksum_code32(string $code): string
             }
         }
 
-        return (string)$s % 10;
+        return (string)($s % 10);
     }
 }

src/Types/TypeInterleaved25Checksum.php

@@ -86,6 +86,6 @@ protected function getChecksum(string $code): string
             $r = (10 - $r);
         }
 
-        return $r;
+        return (string)$r;
     }
 }