Fix misleading error message (#3183)

## Motivation

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## Proposal


Corrected error message in the Message::Swap handler so that it reflects
the swap operation rather than adding liquidity.

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- Nothing to do / These changes follow the usual release cycle.
- These changes should be backported to the latest `devnet` branch, then
    - be released in a new SDK,
    - be released in a validator hotfix.
- These changes should be backported to the latest `testnet` branch,
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    - be released in a validator hotfix.
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and release a new
      SDK soon.

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- [reviewer
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Author: intls

examples/amm/src/contract.rs

@@ -70,7 +70,7 @@ impl Contract for AmmContract {
                 // It's assumed that the tokens have already been transferred here at this point
                 assert!(
                     input_amount > Amount::ZERO,
-                    "You can't add liquidity with zero tokens"
+                    "You can't swap with zero tokens"
                 );
 
                 assert!(input_token_idx < 2, "Invalid token index");