Fix sporadic test failing with OOM

[ggivo]

Missing AuthXManager shutdown in tests causes the token renew thread to run after the test completion.
When used with Mockito.mock() this leads to a growing number of mocked objects and eventually to OOM.

• Invoke AuthXManager.close()
• Updated GitHub test workflow to publish heap dump on OOM errors in the test

[sazzad16]

All these .close(); and .stop(); will still be missed if there are errors; i.e. assertion failures before them.
These should be put in reasonable finally block. try-with-resources can also be considered if possible.