set borsh version to 1.2.1 to match version in solana

pythnet/pythnet_sdk/Cargo.toml

@@ -17,7 +17,7 @@ solana-program = ["dep:solana-program", "dep:anchor-lang"]
 
 [dependencies]
 bincode = "1.3.1"
-borsh = { version = "1.5.1", features = ["unstable__schema"] }
+borsh = { version = "1.2.1", features = ["unstable__schema"] }
 bytemuck = { version = "1.11.0", features = ["derive"] }
 byteorder = "1.4.3"
 fast-math = "0.1"