Add `.avif` to image filetype #87

Job	Run time
Ensure 'cargo fmt' has been run	13s
Extract crate metadata	8s
Minimum supported rust version	4m 39s
aarch64-unknown-linux-gnu (ubuntu-20.04)	2m 26s
arm-unknown-linux-gnueabihf (ubuntu-20.04)	1m 59s
arm-unknown-linux-musleabihf (ubuntu-20.04)	1m 56s
i686-pc-windows-msvc (windows-2019)	2m 38s
i686-unknown-linux-gnu (ubuntu-20.04)	1m 22s
i686-unknown-linux-musl (ubuntu-20.04)	1m 40s
x86_64-apple-darwin (macos-12)	2m 6s
x86_64-pc-windows-gnu (windows-2019)	3m 52s
x86_64-pc-windows-msvc (windows-2019)	5m 34s
x86_64-unknown-linux-gnu (ubuntu-20.04)	1m 20s
x86_64-unknown-linux-musl (ubuntu-20.04)	2m 4s
	31m 57s

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