Use jpeg source files as fallback rather than converting to png (#9010)

Co-authored-by: Erika <[email protected]>

.changeset/quiet-games-film.md

@@ -0,0 +1,5 @@
+---
+"astro": minor
+---
+
+The `<Picture />` component will now use `jpg` and `jpeg` respectively as fallback formats when the original image is in those formats. 

packages/astro/components/Picture.astro

@@ -17,8 +17,9 @@ const defaultFallbackFormat = 'png' as const;
 // Certain formats don't want PNG fallbacks:
 // - GIF will typically want to stay as a gif, either for animation or for the lower amount of colors
 // - SVGs can't be converted to raster formats in most cases
+// - JPEGs compress photographs and high-noise images better than PNG in most cases
 // For those, we'll use the original format as the fallback instead.
-const specialFormatsFallback = ['gif', 'svg'] as const;
+const specialFormatsFallback = ['gif', 'svg', 'jpg', 'jpeg'] as const;
 
 const { formats = defaultFormats, pictureAttributes = {}, fallbackFormat, ...props } = Astro.props;