bridges: add missing crate descriptions (#1919)

Adds descriptions needed for publishing bridges crates to crates.io.

see https://forum.parity.io/t/crates-need-descriptions/2115

Signed-off-by: Adrian Catangiu <adrian@parity.io>

bridges/primitives/test-utils/Cargo.toml

@@ -1,6 +1,7 @@
 [package]
 name = "bp-test-utils"
 version = "0.1.0"
+description = "Utilities for testing substrate-based runtime bridge code"
 authors.workspace = true
 edition.workspace = true
 license = "GPL-3.0-or-later WITH Classpath-exception-2.0"