fix: broken link for on-chain transfer hook example (solana-labs#7041)

Author: jim4067

docs/src/token-2022/extensions.mdx

@@ -1536,7 +1536,7 @@ interact with a program that implements transfer-hook in the repository's
 
 The `spl-transfer-hook-interface` library provides offchain and onchain helpers
 for resolving the additional accounts required. See
-[invoke.rs](https://github.com/solana-labs/solana-program-library/tree/master/token/transfer-hook/interface/src/invoke.rs)
+[onchain.rs](https://github.com/solana-labs/solana-program-library/blob/master/token/transfer-hook/interface/src/onchain.rs)
 for usage on-chain, and
 [offchain.rs](https://github.com/solana-labs/solana-program-library/tree/master/token/transfer-hook/interface/src/offchain.rs)
 for fetching the additional required account metas with any async off-chain client