bug#30872: 26.0.91; odd byte compile issue

[Aaron Jensen]

I realized I left it for the reader to figure out what the issue is.
It appears that using a certain combination of macros, when a file is
byte compiled, that version does not allow you to `setq' a variable
that has been defined by `pcase-let' in an `or'.

The repro demonstrates this by doing a `(setq params nil)' and then
printing the value of params and returning it. It is not set to `nil'
even though that line has been evaluated.

Hope that helps.