CI - fix running phpunit in appveyor

It prints file content
https://ci.appveyor.com/project/zdenekdrahos/phpqa/builds/52238538#L355
https://ci.appveyor.com/project/zdenekdrahos/phpqa/builds/52243499#L32234

Author: zdenekdrahos

tests/.appveyor/.phpqa.yml

@@ -14,7 +14,7 @@ phpcs:
             full: phpcs-full.txt
 
 phpunit:
-    binary: ../../vendor/bin/phpunit.bat
+    binary: ../../vendor/phpunit/phpunit/phpunit
     config: ../../phpunit.xml
     reports:
         file: