chore: remove 'c' from knip.jsonc extension

[JoshuaKGoldberg]

PR Checklist

• Addresses an existing open issue: fixes 🛠 Tooling: End-to-end failures on main for create #1246
• That issue was marked as status: accepting prs
• Steps in CONTRIBUTING.md were taken

Overview

I don't know why the trailing comma is happening... but there's no need for the file to be .jsonc anyway. It only used to have comments.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (6774141) 94.81% compared to head (5c21520) 94.81%.
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1247   +/-   ##
=======================================
  Coverage   94.81%   94.81%           
=======================================
  Files         104      104           
  Lines        5804     5804           
  Branches      492      492           
=======================================
  Hits         5503     5503           
  Misses        300      300           
  Partials        1        1           

Flag	Coverage Δ
create	70.07% <20.00%> (ø)
initialize	42.26% <80.00%> (ø)
migrate	69.88% <20.00%> (ø)
unit	75.59% <80.00%> (ø)

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[github-actions]

🎉 This is included in version v1.54.1 🎉

The release is available on:

• GitHub releases
• npm package (@latest dist-tag)

Cheers! 📦🚀