Check if our CI configuration is potentially causing our intermittent failures

[maspe36]

As discussed in the March 11th monthly meetup, we have some occasional unit test failures. These failures have seemingly been narrowed down to rclrs_tests and appear to be related to DDS usage. See #364 for more details.

With that in mind, it is imperative that we take multiple approaches to thoroughly investigate and analyze the root causes of these failures.

For this issue, we agreed that it would be beneficial to do some research on using shared memory in a unit test that runs in CI. We assume that shared memory requires some form of process isolation, so presumably someone else (another client library) has faced and solved these issues.

Note from RTI on this https://community.rti.com/forum-topic/process-isolation-when-testing-dds-code

[maspe36]

I didn't get around to digging too deep here, but I have been unable to reproduce the intermittent failures locally since #372. Closing for now.