[mono] Time-outs on Linux FullAOT Mono runtime tests CI

On the `runtime-llvm` rolling-builds, the Mono FullAOT runtime test jobs are timing out due to the AOT test compilation taking more than 6 hours.

All rolling-build on main are failing at least since 31st of March (https://dev.azure.com/dnceng-public/public/_build?definitionId=157&_a=summary).