Remove extra "the"

[ibesora]

Noticed there were a couple of extra "the" in the documentation (i.e. in https://maplibre.org/maplibre-style-spec/sky/#sky-horizon-blend)

This PR removes them

Launch Checklist

• Confirm your changes do not include backports from Mapbox projects (unless with compliant license) - if you are not sure about this, please ask!
• Briefly describe the changes in this PR.
• Link to related issues.
• Include before/after visuals or gifs if this PR includes visual changes.
• Write tests for all new functionality.
• Document any changes to public APIs.
• Post benchmark scores.
• Add an entry to CHANGELOG.md under the ## main section.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.78%. Comparing base (f5afe41) to head (aff49c9).
Report is 11 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #922   +/-   ##
=======================================
  Coverage   92.78%   92.78%           
=======================================
  Files         107      107           
  Lines        4739     4739           
  Branches     1346     1346           
=======================================
  Hits         4397     4397           
  Misses        342      342           

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[HarelM]

Thanks!