A smattering of `-Wmissing-field-initializers` fixes #7889

Job	Run time
Get the latest prelude hash	5s
build (ubuntu-22.04, aarch64-unknown-linux-gnu, true)	11m 38s
build (ubuntu-22.04, aarch64-unknown-linux-musl, true)	11m 48s
build (ubuntu-22.04, x86_64-unknown-linux-gnu)	10m 57s
build (ubuntu-22.04, x86_64-unknown-linux-musl, true)	11m 25s
build (macos-13, aarch64-apple-darwin, true)	16m 17s
build (macos-13, x86_64-apple-darwin)	15m 2s
build (windows-2022, x86_64-pc-windows-msvc, true)	17m 59s
Check if there's a release for this half of the month already	2s
Release `latest` tag	23s
Publish buck2.build	2m 23s
Release bi-monthly tag	0s
	1h 37m 59s

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