Increase osx-arm64 GCStress3 timeout

[BruceForstall]

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[BruceForstall]

/azp run runtime-coreclr gcstress0x3-gcstress0xc

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Azure Pipelines failed to run 1 pipeline(s).

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[BruceForstall]

/azp run runtime-coreclr gcstress0x3-gcstress0xc

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[BruceForstall]

Even with this change, there are still osx-arm64 timeouts in GCStress=3 runs.

With all those runs, I see a maximum "Delay" of 23m. That doesn't seem too bad.

I see a maximum "Duration" of over 8hrs. (and killed for timeout) for a number of jobs:

Directed_2.0.1
JIT.Generics.0.1
JIT.opt.0.1
Methodical_d1.0.1
Regression_4.0.10
threading_group2.0.1

This is slightly better than before, but there is obviously still a problem.