[ENH] Clarify that task label is not required to derive from TaskName

[effigies]

Following up on decision made in Copenhagen. This "is" was interpreted by some to be a requirement, but this has never been validated, would be breaking to turn into an error, and is impractical to encode in the schema. Rather than contort ourselves to devise a check, it makes more sense to use RFC 2119 language to make clear that this is an optional convention, not a requirement.

Closes #2081.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.71%. Comparing base (db1c087) to head (eef53a0).
⚠️ Report is 147 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2179   +/-   ##
=======================================
  Coverage   82.71%   82.71%           
=======================================
  Files          20       20           
  Lines        1608     1608           
=======================================
  Hits         1330     1330           
  Misses        278      278           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[neuromechanist]

LGTM.
Actually, I had someone reach out about this very sentence separately, agreed that May works best

[tsalo]

This change makes sense to me.