Mysql - Fix field trait item types

[kouz75]

Iterating over a select field on MySQL throws a fatal error

On SQLite, JSON is decoded as strings → current() returns string → no error.
On MySQL, JSON integers are decoded as PHP int → current() returns int
→ type error against the declared Field|string return type.

To reproduce

Content type

homepage:
    name: Homepage
    singular_name: Homepage
    fields:
        related_entry:
            type: select
            values: entries/{title}

Twig
{{dump(record.related_entry)}}

Error
An exception has been thrown during the rendering of a template ("Bolt\Entity\Field\SelectField::current(): Return value must be of type Bolt\Entity\Field|string, int returned") in index.twig at line 10.

[bobvandevijver]

Ah, can you rebase this on 6.1? 6.2 will be for the Vue upgrade, but I needed to make that the main branch to convince dependabot to use that branch for its updates...

[bobvandevijver]

@kouz75 Something went wrong with the rebase, can you check that?