Fix signature detection on Excel2003XML

Signature can be with single quotes:
```
<?xml version='1.0'?>
<?mso-application progid='Excel.Sheet'?>
```

src/PhpSpreadsheet/Reader/Excel2003XML.php

@@ -82,6 +82,7 @@ class Excel2003XML extends BaseReader implements IReader
         // Read sample data (first 2 KB will do)
         $data = fread($fileHandle, 2048);
         fclose($fileHandle);
+        $data = strtr($data, "'", '"'); // fix headers with single quote
 
         $valid = true;
         foreach ($signature as $match) {