S2AHandshakerServiceChannelTest.newCall_performSimpleRpcSuccess is flaky

[ejona86]

@rmehta19, please address this.

From https://github.com/grpc/grpc-java/actions/runs/11115729476/job/30884701497?pr=11578#step:7:1656 :

S2AHandshakerServiceChannelTest > newCall_performSimpleRpcSuccess FAILED
    java.io.IOException: Failed to bind to address 0.0.0.0/0.0.0.0:36363
        at io.grpc.netty.shaded.io.grpc.netty.NettyServer.start(NettyServer.java:333)
        at io.grpc.internal.ServerImpl.start(ServerImpl.java:185)
        at io.grpc.internal.ServerImpl.start(ServerImpl.java:94)
        at io.grpc.s2a.channel.S2AHandshakerServiceChannelTest.setUp(S2AHandshakerServiceChannelTest.java:65)

        Caused by:
        io.grpc.netty.shaded.io.netty.channel.unix.Errors$NativeIoException: bind(..) failed: Address already in use

Looks like both servers in the test unnecessarily use Utils.pickUnusedPort(). As I mentioned in #11537 , pickUnusedPort is inherently racy. These usages should be changed to 0 to let start() choose the port which isn't racy.

[rmehta19]

Thanks for bringing this up, addressed in #11601