Disable Apline.38 ARM64 runs

[jaredpar]

These are consistently failing on all runs. Disabling to get the build
green again while we dig into this

#1871

[sdmaclea]

LGTM

[safern]

As a note this is not the best way to disable test runs because the test runs still try to send to helix but with an empty set of queues, causing the build to fail with error:

You must specify at least one target queue to send a job to helix. Use the HelixTargetQueues property or HelixTargetQueue items.

https://dev.azure.com/dnceng/public/_build/results?buildId=497977

Libraries run-test-job.yml is not resilient to empty helix queues as coreclr's ones. I don't like skipping the send to helix step when there are no queues because that's prone to errors if by mistake we aren't passing the right queues to a job we want to run and it would take a while to notice.

The way I would recommend to disable test runs in the future if by commenting directly in runtime.yml the platform entry, in this case I would've commented this:
https://github.com/dotnet/runtime/blob/master/eng/pipelines/runtime.yml#L563

The issue referenced on this PR, will soon be fixed, so there is no point on sending a PR to fix this new error and instead wait for the fix which will be sent soon and re-enable the queues setup.

[jaredpar]

The way I would recommend to disable test runs in the future if by commenting directly in runtime.yml the platform entry, in this case I would've commented this

That line you linked is the following:

 helixQueuesTemplate: /eng/pipelines/libraries/helix-queues-setup.yml

Did you mean to comment out that line?

[safern]

No sorry about that, I meant this line:

runtime/eng/pipelines/runtime.yml

Line 560 in 6a8603b

- Linux_musl_arm64

[jaredpar]

Gotcha. That makes sense. Essentially kill teh platform at the higher level.

[safern]

Essentially kill teh platform at the higher level.

Exactly.