doc: fix typographical error in fixtures README

[Trott]

Fixing a typo. Although it looks like this file comes from https://github.com/tc39/source-map-tests. Did we ever get tooling in place to sync from there?

[Trott]

(Mostly opening this to test the GitHub bot is still working, since I merged a dependency update. As long as the bot labels it, it's fine to close it. I'm not invested in it. Although we should definitely get that update-tooling together. Or if it's already in place, run it.)

[Trott]

Closing in favor of #60978

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.53%. Comparing base (37d9cfc) to head (a9dbaae).
⚠️ Report is 8 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #60977      +/-   ##
==========================================
+ Coverage   88.51%   88.53%   +0.01%     
==========================================
  Files         703      703              
  Lines      208430   208430              
  Branches    40198    40199       +1     
==========================================
+ Hits       184491   184531      +40     
+ Misses      15951    15898      -53     
- Partials     7988     8001      +13     

see 44 files with indirect coverage changes

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