PHPUnit 9 comes with various changes in the XML
configuration file, namely:
- the old "filter" section has been renamed to "coverage".
- "whitelist" has been renamed to "include"
- "exclude" is not a child of "include" anymore, but of "coverage".
- "include" cannot have configuration attributes anymore, only
"coverage" can"
Visually it means that the old section (invented example):
```
<filter>
<whitelist attributes_may_go_here="xx">
<directory suffix=".php">classes</directory>
<directory suffix=".php">externallib.php</directory>
<exclude>
<directory suffix="_test.php">.</directory>
</exclude>
</whitelist>
</filter>
```
Now looks like:
```
<coverage attributes_may_go_here="xx">
<include>
<directory suffix=".php">classes</directory>
<directory suffix=".php">externallib.php</directory>
</include>
<exclude>
<directory suffix="_test.php">.</directory>
</exclude>
</filter>
```
So, switching to the new xsd so we can validate the remaining changes.
