fix: update broken ethereumbook link to new chapter structure

The ethereumbook repository was restructured - the old path
04keys-addresses.asciidoc no longer exists. Updated to the
new chapter_4.md which contains the same Ethereum addresses
documentation.

vendor/pezkuwi-subxt/signer/src/eth.rs

@@ -442,7 +442,7 @@ mod test {
 
 		#[test]
 		fn check_account_id(keypair in keypair()) {
-			// https://github.com/ethereumbook/ethereumbook/blob/develop/04keys-addresses.asciidoc#ethereum-addresses
+			// https://github.com/ethereumbook/ethereumbook/blob/develop/src/chapter_4.md
 			let account_id = {
 				let uncompressed = keypair.0.0.public_key().serialize_uncompressed();
 				let hash = keccak(&uncompressed[1..]).0;