ci: changes Slack deployment message channel

[matt-frizzell]

Changes the Slack channel for deployment messages to the new mobile-deployments channel

See customerio/issues#9014

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[ami-oss-ci]

Pull request title looks good 👍!

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[levibostian]

Updated base branch from develop to main because we are deleting the develop branch.

Since main and develop both have the same branches in them, the file changes in this PR are the same after updating the base branch.

[levibostian]

I don't see much value in having slack deployment messages for RH app. Also because we are deprecating the app, I think it's better for us to disable slack messages instead of trying to modify them.

Closing. Re-open if someone believes this still adds value.