[experimental] Avoid bug in fetch() with non-object reasons thrown with AbortSignal

[steveluscher]

Overview

The AbortSignal reason can be whatever you want, but there's a bug in undici <6.7.0 that chokes on signal reasons that are not objects. Read all about the fix here: nodejs/undici#2833

We need to make sure that none of our reasons trigger this bug or we're incompatible with undici <6.7.0 and >6.?.?. In my testing this only blows up in Node 21.

[github-actions]

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