TLDR: All things here are generated, open issues in the rust-skia repository.
This repository's releases tab contains binary builds for Skia, the skia-bindings library, and the Rust bindings src/bindings.rs. These files are generated on the CI server in the rust-skia repository for each commit to the release branch.
If the platform, configuration, and feature set matches, official skia-bindings crates will automatically download the binaries that were generated with the same hash. If no binary is available, a full build of Skia, the skia-bindings library, and the src/bindings.rs file will be triggered.