`SupervisorSuite` timeout on Windows

[djspiewak]

Looks like VM slowness to me:

[error] ==> X cats.effect.std.SupervisorSuite.concurrent - restart / cancel race  20.056s cats.effect.TestTimeoutException: test timed out after 20 seconds
[error]     at cats.effect.Runners.$anonfun$timeout$1(Runners.scala:151)
[error]     at cats.effect.unsafe.WorkStealingThreadPool$$anon$1.apply(WorkStealingThreadPool.scala:695)
[error]     at cats.effect.unsafe.WorkStealingThreadPool$$anon$1.apply(WorkStealingThreadPool.scala:692)
[error]     at cats.effect.unsafe.WorkerThread.run(WorkerThread.scala:908)

[durban]

Which branch?

Possibly related: #4446.

[djspiewak]

Almost positive this was series/3.x