fix: image optimization typo (#5328)
fix typo: Ecoding => Encoding
### Description
Fixed error description of uncompiled image formats
  I ran into this error while trying to load the an image in the
GIF format, which doesn't seem to be supported yet. 
### Testing Instructions
Load an image with next/image with an unsupported format, such as GIF
Co-authored-by: Anthony Shew <anthony.shew@vercel.com>
