Build/Test Tools: Correct the Multisite PHPUnit log path.

The `tests/phpunit` part of the logging file path in the `multisite.xml` configuration file is unnecessary because it already exists within that directory.

See #64894.

git-svn-id: https://develop.svn.wordpress.org/trunk@62464 602fd350-edb4-49c9-b593-d223f7449a82

Author: desrosj

tests/phpunit/multisite.xml

@@ -74,6 +74,6 @@
 		</whitelist>
 	</filter>
 	<logging>
-		<log type="junit" target="tests/phpunit/build/logs/junit.xml" />
+		<log type="junit" target="build/logs/junit.xml" />
 	</logging>
 </phpunit>