This prevent a false-positive warning about a vulnerable loofah version.
We also need to ignore a new warning, about an unsafe redirect. This is
unsafe when the object given in redirect can be a hash that includes
a `:host` key. But here we are redirecting to a plain string, which is
definitely safe.
The `joins` are declared explicitely in order to associate a predictable
name to the joined table.
Otherwise, when the query is joined with `:users`, ActiveRecord will
alias the join automatically to solve the conflict. Unfortunately, the
automatic resolution means that the table name becomes unpredictable,
and thus unsuitable to perform queries on.
