[harbour-validator] Allow python3-sqlite. Fixes JB#51431

[vigejolla]

Previously python3-sqlite was included in python3 package, so it was
not necessary to install it separately. Now that it is a separate
package we need to allow it in dependencies.

[pvuorela]

In a way it would be nice if we handled the base python automatically, python3-sqlite would be automatically installed with the python support as that's the way it used to be and wouldn't require adaptation from apps at all.

Then again allowing to depend explicitly on the sqlite package shouldn't do much harm either so LGTM.

Btw, interesting that we don't allow python3 itself explicitly(?) Not that we necessarily should, the packaging with -base and -libs feels a bit messy. Perhaps sould have just "python3".