CI doesn't run unit tests for non-default features

[Michael-F-Bryan]

Describe the bug

It doesn't look like our current CI system runs unit tests for code hidden behind feature flags. That means issues like #3795 can slip in because we don't have full test coverage.

For example, between #3795 and #3739, trying to execute unit tests for the runners in the wasmer-wasix crate (i.e. cargo test --features webc_runner,webc_runner_rt_wasi,webc_runner_rt_wcgi) would fail to build because we'd introduced a !Send+!Sync field to WcgiRunner and the test was passing a WcgiRunner instance to another thread.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[theduke]

Not stale.

[stale]

Feel free to reopen the issue if it has been closed by mistake.