Mattermost-server: Migrate tests from "api4/webhook_test.go" to use testify

[mattermod]

Mattermost is migrating its server tests from using the t.Fatal method calls on their checks to use the testify toolkit. The goal of this migration is to improve the readability of the tests, making them more concise and meaningful. This Help Wanted issue is to migrate the tests in the api4/webhook_test.go file.

The expected way to migrate this is to go to the api4/webhook_test.go file and modify the calls to t.Fatal and the condition checks that lead to them, replacing them with calls to the the require package if a failure should stop the execution of the test, or the assert package if it shouldn't.

Example: mattermost/mattermost-server#12039

If you have questions about the ticket or you need any help, feel free to contact miguel.delacruz or jesus.espino in https://community.mattermost.com/

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JIRA: https://mattermost.atlassian.net/browse/MM-19620

[lucianomagrao]

i got this

[drekar]

Looks like we got our wires crossed @lucianomagrao. I had accepted issues #12860-12869, but for some reason the update didn't take on this one, and I did it anyway. I'm deleting my PR because yours is already approved.

[saturninoabril]

@lucianomagrao PR has been merged. Thank you for your contribution!