Update link in docs to offchain message spec (#7982)

docs/src/cli/examples/sign-offchain-message.md

@@ -97,4 +97,4 @@ with a fixed prefix: `\xffsolana offchain`, where first byte is chosen such
 that it is implicitly illegal as the first byte in a transaction
 `MessageHeader` today. More details about the payload format and other
 considerations are available in the
-[proposal](https://github.com/solana-labs/solana/blob/master/docs/src/proposals/off-chain-message-signing.md).
+[proposal](https://github.com/anza-xyz/agave/blob/master/docs/src/proposals/off-chain-message-signing.md).