tone down global install warning

[davidjgoss]

🤔 What's changed?

• Tweak the wording of the global install warning to be less severe
• Only do the check and warning if debug is enabled

⚡️ What's your motivation?

Fixes #2274 - since this can be a false positive, and the issues stemming from it are now much more obvious and actionable than they used to be, we don't need this to be prominent any more.

🏷️ What kind of change is this?

• :bank: Refactoring/debt/DX (improvement to code design, tooling, documentation etc. without changing behaviour)
• :bug: Bug fix (non-breaking change which fixes a defect)

📋 Checklist:

• [x] I agree to respect and uphold the Cucumber Community Code of Conduct
• [x] I've changed the behaviour of the code
  • [ ] I have added/updated tests to cover my changes.
• [x] My change requires a change to the documentation.
  • [x] I have updated the documentation accordingly.
• [x] Users should know about my change
  • [x] I have added an entry to the "Unreleased" section of the CHANGELOG, linking to this pull request.

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[coveralls]

Coverage: 98.49% (+0.001%) from 98.489% when pulling 17bd8193e59cce0e0cb41845817302564de75fff on fix/tone-down-global-warning into 728fe26f9946025946452e73ef615f5488c0e533 on main.