v2.0.0-rc.21

Upgrade Specta to solve #153.

Due to changes that were merged into Tauri this release will be broken until tauri-apps/tauri#12371 is released. In the meantime you can use the following patch:

[patch.crates-io]
# Waiting for release of https://github.com/tauri-apps/tauri/pull/12371
tauri = { git = "https://github.com/tauri-apps/tauri", rev = "75d56e8364fb203387bb5a5235f316dd7dfa6acd" }