Update versions to 0.21.3

Author: sdroege

Cargo.lock

@@ -27,7 +27,7 @@ exclude = ["gir", "checker"]
 [workspace.package]
 homepage = "https://gtk-rs.org/"
 authors = ["The gtk-rs Project Developers"]
-version = "0.21.2"
+version = "0.21.3"
 repository = "https://github.com/gtk-rs/gtk-rs-core"
 license = "MIT"
 exclude = ["gir-files/*"]