Mattermost-server: Migrate tests from "web/oauth_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 web/oauth_test.go file.

The expected way to migrate this is to go to the web/oauth_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-19462

[bensooraj]

I can take this up!

[bensooraj]

I have raised a PR for #12816.

[jasonblais]

This is back up for grabs, here's start of a PR for reference: https://github.com/mattermost/mattermost-server/pull/12816

[nadalfederer]

can I take this