[IGNORE] Execute incident tests based on a manifest

[ben-c-at-moz]

Relevant Links

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Description of Code / Doc Changes

• Create a manifest for the tests we run in incident (manual-flow) testing
• Modify choose_ci_set to work with manifest files
• Modify the workflow to work with these changes
• Lint

Process Changes Required

Mark the relevant boxes:

• Changes CI flow
• Changes scheduled Beta or DevEdition

Screenshots or Explanations

The manifest looks like this:

suite:
  test_1: pass
  test_2: unstable
  test_3: xfail
  test_4:
    win: pass
    mac: unstable
    linux: xfail
  test_5: pass

Comments or Future Work

We should consider moving all of our scheduled flows to using manifests, and potentially reworking choose_ci_set to write a manifest rather than its current output

Workflow Checklist

• Please request reviewers
• If this is an unblocker, please post in Slack.
• If asked to address comments, please resolve conversations.
• If asked to change code, please re-request review from the person who wanted changes.

Thank you!