rubocop fix: Invert if/else condition notification_channel

[Sayak-singha]

Signed-off-by: Sayak Singha 69098567+Sayak-singha@users.noreply.github.com

Fixes #11418

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Code Climate has analyzed commit 644652f and detected 0 issues on this pull request.

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[github-actions]

This pull request generated screenshots of many common pages in the running app. You should be able to download and view them here:
https://github.com/publiclab/plots2/suites/8318361731/artifacts/365359552

[TildaDares]

Amazing work @Sayak-singha. Thank you!!

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[TildaDares]

Congratulations on merging your PR @Sayak-singha 🎉🎉

[Sayak-singha]

Congratulations on merging your PR @Sayak-singha 🎉🎉

Thanks a lot