Fix JDK 6 compile break from added fetch tests

The Java 6 compiler fails to compile the test because there is an
ambiguous method signature defined for two of the fetch methods.

The methods which are ambiguous are:

    fetch(String, RefSpec)

    fetch(String, RefSpec ...)

Java 7 seems to resolve a method reference fetch(String, RefSpec) to
call the fetch(String, RefSpec ...) method.