Correct unit test for gen_nondet_string

The "java::" prefix was missing from the previous implementation and
this is now fixed.

Author: romainbrenguier

unit/java_bytecode/java_object_factory/gen_nondet_string_init.cpp

@@ -79,7 +79,7 @@ SCENARIO(
           "return_array = cprover_associate_length_to_array_func"
           "(nondet_infinite_array, tmp_object_factory);",
           "arg = { [email protected]={ .@class_identifier"
-          "=\"java.lang.String\", .@lock=false },"
+          "=\"java::java.lang.String\", .@lock=false },"
           " .length=tmp_object_factory, "
           ".data=nondet_infinite_array };"};