Fix: PublisherZMQ::flush is called after the publisher has been destructed

[Tradias]

There are unfortunately no tests for any of the loggers :(. But adding them seemed out-of-scope for this pr.

Test code:

    static constexpr auto XML = R"(
<root>
    <BehaviorTree>
    <SetBlackboard output_key="arg1" value="1" />
    </BehaviorTree>
</root>
)";
    BT::BehaviorTreeFactory factory;
    auto tree = factory.createTreeFromText(XML);
    BT::PublisherZMQ zmq_logger{tree, 1};
    tree.tickRoot();

Output:

Exception thrown at 0x00007FFE533E4FD9 in test-behavior-tree.exe: Microsoft C++ exception: zmq::error_t at memory location 0x0000005A1F7AEB40.
[PublisherZMQ] Publisher quitting.
[PublisherZMQ] just died. Exception Context was terminated
Exception thrown at 0x00007FF659E7124F in test-behavior-tree.exe: 0xC0000005: Access violation reading location 0xFFFFFFFFFFFFFFFF.

[facontidavide]

Hopefully closed by #440

[Tradias]

Looks like #440 was never actually compiled by the CI.

[Tradias]

@facontidavide I made the necessary changes to the pipeline. It now actually runs gtest_logger_zmq test. This pr is therefore ready from my side.