[BUG]: build warnings due to HEIF avatar file format

[natevw]

Noticed this in the build log:

12:02:46 PM: warning You can't use childImageSharp together with 0xepley.heif — use publicURL instead. The childImageSharp portion of the query in this file will return null:
/opt/build/repo/src/pages/register.tsx

Not sure how much practical impact this has but I wonder if we should convert that to a better-supported format and/or try avoid merging HEIF images in the future?