fix: warning for .svg images on sourcing

[julrich]

The following warning is displayed for every sourced .svg image:

warn You can't use childImageSharp together with quote-dark.svg — use publicURL instead. The childImageSharp portion of the query in this file will return null: undefined

Maybe there's a fix for it? Like a conditional fragment, or something? Because image type for Markdown / Frontmatter fields can be either (rasterized vs svg).