Fix #61094 Wrong WSDL cache file name

WSDL cache files are created with the format wsdl-owner_username-uri_md5sum
and with permission 0600. This will result in an error when two or more
users are trying to run the same script that uses the same wsdl: only the
first user can access to the wsdl cache file, while a second user will
encounter a SOAP-ERROR complaining about not being about to load the WSDL.
The bug was introduced in commit 1a9e668a04 which was supposed to use getuid()
instead of php_get_current_user() in the cache filename.