Sparse checkout errors sporadically in CI

[m-nash]

https://dev.azure.com/azure-sdk/public/_build/results?buildId=3624149&view=logs&j=51b3775a-1644-5866-7147-5315708e6c48&t=25d16842-582d-5a38-69fc-328226e341e6&l=27

[benbp]

We've been seeing these github timeouts lately, they seem to be concentrated on mac agents.

Error for posterity:

git -c advice.detachedHead=false checkout f46af6905e9370aed03578e6fc4ec76249c8a64d --
fatal: unable to access 'https://github.com/Azure/azure-sdk-for-net/': Recv failure: Operation timed out
fatal: could not fetch fbfa86eb878a414caeb5e0ab7d1020d13ea5a9e4 from promisor remote

##[error]PowerShell exited with code '1'.

[danieljurek]

Mac hosted agents aren't hosted in Azure Datacenters. They're hosted in GitHub datacenters. This means that these agents could be impacted by a combination of factors including both Azure and GitHub connectivity.

Since these issues relate to network connectivity and don't directly test SDK/product functionality, I think a reasonable thing to do here would be to detect these kinds of failures (either by checking exit codes or the outputs) and re-trying, after a delay, on failures that could be transient.

[benbp]

@danieljurek #8019

[weshaggard]

Closing as #8019 added retries which seem to have helped with this.