Add missing tests for the traceable cache adapters

[ste93cry]

I just noticed that somehow I missed to make the unit tests for the traceable cache adapters, so here they are 😃

[Jean85]

CI is broken though... does #487 fix it?

[ste93cry]

That PR helps fixing the build here by fixing the conditions needed to auto-enable the tracing instrumentation for the Cache component, which in turn allows me to safely require the symfony/cache-contracts package used in the unit tests without affecting whether the enablement status of the tracing feature. TL;DR: partially, yes