Cache: immediate eviction in net4 tests

[majocha]

Description

I'm noticing some CI hangs on .Net Framework tests after #18875

The cause may or may not be thread pool starvation: old .Net uses different algorithms and does not ramp up threads fast enough.

Specifically after #18875 the type subsumption cache is tied to TcGlobals, which means more instances instead of one per process singleton. Unfortunately, in tests it means thousand started in quick succession. So, the queued eviction for each one eats some threads, quickly.

So, if the problem persists, this should be a fix.

[github-actions]

❗ Release notes required

@majocha,

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[majocha]

I think this is needed after all.