[CI] Add check to GEF to validate GEF-Extras too

[hugsy]

Type of feature request

None

Misc

No response

Summary Description

To avoid situations where users complain about recent changes to GEF that got to break Extras, add a CI test to load & run in GEF the tests from Extras/main.

Implementation idea/suggestion

see above

Existing alternatives?

No response

Additional information

No response

[hugsy]

Also make install scripts point to the latest release for both gef & extras

Done with #1007