debugging CI issues

[timotheecour]

when a problem can't be reproduced locally and needs to be debugged in CI, try this:

• disable all CI except 1 to have faster turnaround and avoid too much CI usage; can be done via:
• rm -rf .builds/
• rm -rf .github/workflows
• in azure-pipelines.yml, comment out all except 1 elements of matrix, eg:

      OSX_amd64:
        vmImage: 'macOS-10.15'
        CPU: amd64

• in koch.nim in runCI, skip whatever can be skipped to go straight to the thing that causes problems; eg see commented out code:

  when false: # debugging: when you need to run only 1 test in CI, use something like this:
    execFold("debugging test", "nim r tests/stdlib/tosproc.nim")
    doAssert false, "debugging only"

links

• see also: https://nim-lang.github.io/Nim/contributing.html#the-cmdgit-stuff-debugging-ci-failures-flaky-tests-etc