CI: run a single testcase as sanity-check

[jori-nordic]

In order to prevent regressions to the framework or shared code, it would be nice if there was a mandatory check for running at least one PTS test-case before allowing PRs to be merged. Although it will not catch all errors, it would provide a good sanity-check, at minimal cost.

It could be a CI step that is only triggerable by codeowners for security and resource utilization concerns.

[jori-nordic]

As discussed on the Zephyr Bluetooth WG meeting @sjanc @carlescufi