Recognize webp as a valid image format

[khiga8]

Description

Checklist:

• I am adding a new extension to a language.

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      • [URL to each sample source, if applicable]
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[Alhadis]

The array that you're modifying… does it influence which filetypes are "viewable" as images on GitHub? If so, you should consider supporting other image formats that are supported by browsers (either contemporaneously or historically) but not rendered by the site's file-viewer:

    def image?
      %w[
          .apng .avif .bmp .cur .gif
          .heic .ico .jpg .jpeg .png
          .tif .tiff .webp
      ].include?(extname.downcase)
    end