User admin API returns integers instead of booleans on SQLite, or the documentation is incorrect

[matrixbot]

This issue has been migrated from #13519.

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Similar to #13505.
Originally reported by @jplatte in matrix-org/synapse#13509 (comment):

Description

The first example on https://matrix-org.github.io/synapse/develop/admin_api/user_admin_api.html shows this:

    "is_guest": 0,
    "admin": 0,
    "deactivated": 0,
    "shadow_banned": 0,

but some of these fields are mentioned as being bool further down.