[processing] fix open script dialogs (fix #16347)

[ghtmtt]

Description

Small PR that fixes issue #16347. Ideas taken from b0dc9f8, thanks @nyalldawson :)

Checklist

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[alexbruy]

Wiping ~/.qgis3 fixes this issue without editing code. I think this is related to recent QgsSettings switch, so IMHO there is no sense in this fix.

[ghtmtt]

ah ok, I saw the recent commit b0dc9f8 that fixed almost the same thing for the modeler and I thought it could be useful to fix also for scripts.
Feel free to dump the PR if you think it is useless

[alexbruy]

Sorry, not ~/.qgis3, but QGIS settings.

[ghtmtt]

Ok, you are talking about this qgis/QGIS-Enhancement-Proposals#82 right?
Anyway, no problem, if the PR is useless dump it without problems ;)

[ghtmtt]

@alexbruy can we close or merge this PR?

[ghtmtt]

@alexbruy sorry for writing again. But I freshly recompiled QGIS, opened with the --configpath options but I still get the same error fixed with this PR.
I just don't understand what should I remove for fixing this without code writing. Thanks in advance!