Fix transaction definition setTimeout error message since zero is valid

This commit rephrases the `DefaultTransactionDefinition#setTimeout`
exception message to better reflect the fact that 0 is a valid input
value.

Even though this often leads to a transaction immediately timing out
after opening, there is one notable case where this has another
meaningful effect: in Jakarta transactions (`UserTransaction`), when
passing 0 "the transaction service restores the default value".

Closes gh-32635

spring-tx/src/main/java/org/springframework/transaction/support/DefaultTransactionDefinition.java

@@ -227,7 +227,7 @@ public class DefaultTransactionDefinition implements TransactionDefinition, Seri
 	 */
 	public final void setTimeout(int timeout) {
 		if (timeout < TIMEOUT_DEFAULT) {
-			throw new IllegalArgumentException("Timeout must be a positive integer or TIMEOUT_DEFAULT");
+			throw new IllegalArgumentException("Timeout must be a non-negative integer or TIMEOUT_DEFAULT");
 		}
 		this.timeout = timeout;
 	}