[examples] Changed ChatType from CHANNEL to SUPERGROUP to avoid confusion

[MasterGroosha]

Description

Channels require a separate channel_post_handler, so this example is currently broken and confusing

Type of change

Please delete options that are not relevant.

• Documentation (typos, code examples or any documentation update)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

Manually

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes