Testing: Added mail port to testing env options

Prevents conflict with potential user-set option.
For #5755

Author: ssddanbrown

phpunit.xml

@@ -21,6 +21,7 @@
     <server name="DB_CONNECTION" value="mysql_testing"/>
     <server name="BCRYPT_ROUNDS" value="4"/>
     <server name="MAIL_DRIVER" value="array"/>
+    <server name="MAIL_PORT" value="587"/>
     <server name="MAIL_VERIFY_SSL" value="true"/>
     <server name="LOG_CHANNEL" value="single"/>
     <server name="AUTH_METHOD" value="standard"/>