[mono][infra] FullAOT x64 linux CI jobs are timing out or running very long

[matouskozak]

Almost all recent runs of runtime-llvm contain a cancellation of full AOT x64 linux jobs (RuntimeTests and RuntimeIntrinsicsTests). This makes them unreliable for test coverage as we are not getting the results of failed tests.

We should investigate why the compilation of tests is taking longer now and either fix the issue or increase the timeout limit.

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fyi: @kotlarmilos @steveisok