Incoming Webhooks UI: Configured channel displays as '--- Select a channel ---' if the user is not joined to that channel

[ghost]

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Summary

When viewing an existing incoming webhook in the "Integrations" panel, the "Channel" field is confusingly displayed as --- Select a channel --- if the current user is not joined to that channel.

Steps to reproduce

v5.37.1

• Create a channel aa
• Set up an incoming webhook that has aa as the default channel
• Leave the channel aa
• View the incoming webhook under the "Integrations" -> "Incoming Webhooks" panel

Expected behavior

The user should see the name of the selected channel for the webhook, since it has been configured.

Observed behavior (that appears unintentional)

The user sees --- Select a channel --- which may make them believe that no channel selection has been configured for the webhook.

[amyblais]

Opened a ticket: https://mattermost.atlassian.net/browse/MM-38482