rust-once-cell-1 can't be built because it now depends on rust-parking-lot-core-0.9. This can't be built because it now requires rust-windows-sys-0.36 according to the crates page (https://crates.io/crates/parking_lot_core/0.9.3/dependencies). This package definition can be found in the guix channel that Must Not Be Named (right next to firefox), and is not present in the main guix repo.
I would guess the reasoning behind this is that rust-windows-sys requires some kind of nonfree code in its dependencies (perhaps rust-windows-aarch64-msvc-0.36?). If I'm wrong about this and the package does meet the Guix repo standards, then the alacritty problem can be fixed by incorporating the rust-windows-sys-0.36 package definition into (gnu packages crates-io). Would be happy to add them, but I've never submitted a patch before (would love to start if someone wouldn't mind guiding me!) and I'm new to the mailing list style of repo management. (I notice the rust-windows-sys-0.28 package is included, so I assume bumping the version up to 0.36 will be acceptable. Am testing this locally.)
Otherwise, I believe the guix-repo-only solution requires rolling back the update to rust-once-cell in commit af39bd88a27e33c43df8324202cfebaeeb77437a.