fix the warning in SyncProposalProcessorTest.java

[WARNING] /home/michi/gitdev/jzab/src/test/java/com/github/zk1931/jzab/SyncProposalProcessorTest.java: Some input files use unchecked or unsafe operations.
[WARNING] /home/michi/gitdev/jzab/src/test/java/com/github/zk1931/jzab/SyncProposalProcessorTest.java: Recompile with -Xlint:unchecked for details.