Make ext-salt check more robust. Fixes #1606

Don't assume the exact length of the salt, but just check the prefix.

Author: bgrainger

src/MySqlConnector/Core/ServerSession.cs

@@ -945,8 +945,8 @@ private async Task<PayloadData> SwitchAuthenticationAsync(ConnectionSettings cs,
 				payload = await ReceiveReplyAsync(ioBehavior, cancellationToken).ConfigureAwait(false);
 				var extendedSalt = payload.Span;
 
-				// MariaDB 11.8.4 sends an extra 0x01 byte at the beginning of ext-salt; cf. https://mariadb.com/docs/server/reference/clientserver-protocol/1-connecting/connection#parsec-plugin
-				if (extendedSalt.Length == 21 && extendedSalt[0] == 1 && extendedSalt[1] == 'P')
+				// MariaDB 11.8.4 sends an extra 0x01 byte at the beginning of ext-salt: https://github.com/mysql-net/MySqlConnector/issues/1606
+				if (extendedSalt.Length > 2 && extendedSalt[0] == 1 && extendedSalt[1] == 'P')
 					extendedSalt = extendedSalt[1..];
 
 				Span<byte> combinedData = stackalloc byte[switchRequest.Data.Length + extendedSalt.Length];