feat: add doNotUseFetch helper to the test utils

[galargh]

• Because this PR includes a bug fix, relevant tests have been included.
• Because this PR includes a new feature, the change was previously discussed on an Issue or with someone from the team.
• I didn't do anything of this.

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I found it helpful during the draft implementation of #5774.

The idea is to override the global reference to fetch with a function that always throws an error. This is a very crude approach to simulating network connectivity issues when using fetch. We can explore this area further in the future if needed. However, at this time, this met my needs.

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[alcuadrado]

Interesting PR, I think I'd just rename the path to /http instead of /global, as it'd be easier to discover in the future.

[alcuadrado]

Now that I think of, maybe it'd be better to use a linter rule that directs you to the utils package

[galargh]

Now that I think of, maybe it'd be better to use a linter rule that directs you to the utils package

Do you mean one that does that when someone tries to overwrite global.fetch directly?