…kManager [Up-port] (#3504)

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Up-port of #3502  
Fixes #2539 


## Changelog

- Added: `LocalClientCannotWrite` function to co-locate the shared
functionality
- Fixed: Ensure that the `NetworkManager` exists before attempting to
access the `LocalClientId`

## Testing and Documentation

- No tests have been added.

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## Backport

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Backported in #3502

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Co-authored-by: unity-renovate[bot] <120015202+unity-renovate[bot]@users.noreply.github.com>
Co-authored-by: Emma <emma.mcmillan@unity3d.com>

Adding unreleased changelog set.

…elop-2-0-0

Fixing merge issue with change log.