chore: change release-please to prerelease for v12

[mark-wiemer]

PR Checklist

• Addresses an existing open issue: works on 📌 Mocha 12 Release Plan #5357
• That issue was marked as status: accepting prs
• Steps in CONTRIBUTING.md were taken

Overview

Start prereleasing v12 betas, then RCs, then v12 proper :)

[github-actions]

PR Compliance Checks

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Issue Reference

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The check is looking for a phrase similar to: "Fixes #XYZ" or "Resolves #XYZ" where XYZ is the issue number that this PR is meant to address.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.69%. Comparing base (ca4af43) to head (177b4c5).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5539      +/-   ##
==========================================
- Coverage   93.73%   93.69%   -0.05%     
==========================================
  Files          57       57              
  Lines        4391     4391              
  Branches      850      850              
==========================================
- Hits         4116     4114       -2     
- Misses        275      277       +2     

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[JoshuaKGoldberg]

Whoop! 🙌