ed25519: loosen signature crate dependency again (#598)

Like #582, there is a new release of `signature` (v2.2.0) which contains
no breaking changes from ed25519-dalek's perspective. The main notable
one is it bumps MSRV to 1.60, which so also happens to also be
ed25519-dalek's MSRV.

This commit loosens the version requirement to allow `>=2.0, <2.3` to
allow the `signature` 2.2 series.

ed25519-dalek/Cargo.toml

@@ -28,7 +28,7 @@ features = ["batch", "digest", "hazmat", "pem", "serde"]
 [dependencies]
 curve25519-dalek = { version = "4", path = "../curve25519-dalek", default-features = false, features = ["digest"] }
 ed25519 = { version = ">=2.2, <2.3", default-features = false }
-signature = { version = ">=2.0, <2.2", optional = true, default-features = false }
+signature = { version = ">=2.0, <2.3", optional = true, default-features = false }
 sha2 = { version = "0.10", default-features = false }
 subtle = { version = "2.3.0", default-features = false }