fix for realtime calling subscription multiple time - Appwrite 1.4.x

[lohanidamodar]

What does this PR do?

• Fixes issue with calling subscribe multiple times
• Not syncing with main so this remains, if we want to release Flutter SDK with this fix for Appwrite 1.4.x
• For latest PR check: https://github.com/appwrite/sdk-generator/pull/801
• We shouldn't merge this, rather use this if we want to release (as main has few new features I think not suitable for generating with spec for 1.4.x) if not we can close this issue

Test Plan

• Manually testing the generated SDK

Related PRs and Issues

• https://github.com/appwrite/sdk-for-flutter/issues/156

Have you read the Contributing Guidelines on issues?

YES