chore: 960 - refreshed pubspec.yaml, again

[monsieurtanuki]

What

• Same as chore: 960 - refreshed pubspec.yaml #1021, but with a little twist.
• Looks like recent versions of json_serializable use that brand new stupid syntax with if(... case ...), which is not supported everywhere.
• Therefore, we have to use the best version of json_serializable without that syntax.

Fixes bug(s)

• Fixes: Unable to generate files using build_runner #1023

Part of

• Add new localized ProductField's #960

[PrimaelQuemerais]

This change is required if we are not willing to bump dart to version 3.0.0

[monsieurtanuki]

Thank you @PrimaelQuemerais for your review!