Fix deprecation warning and correctness bug when using arel_extensions >= 2.2

[javieromar7]

Problem

When arel_extensions >= 2.2 is present, extract_correlated_key triggers a deprecation warning on every query involving correlated joins:

DEPRECATION WARNING: `ArelExtensions::Attributes#==` is now deprecated. Use `.eq` instead.
(called from extract_correlated_key at lib/ransack/adapters/active_record/context.rb:215)

Beyond the warning, there is a silent correctness bug: ArelExtensions >= 2.2 overrides == on Arel attributes to return an Arel::Nodes::Equality SQL predicate node — not a boolean. This means the if join_root.left == pk check is always truthy (an Arel node is never nil/false), so join_root.right is returned unconditionally, regardless of whether join_root.left is actually the primary key.

Root cause

# arel_extensions/lib/arel_extensions/attributes.rb
def ==(other)
  deprecated 'Use `.eq` instead.'
  Arel::Nodes::Equality.new self, Arel.quoted(other, self)  # returns an Arel node, not a boolean
end

Fix

Replace == with eql? for the primary key identity check. Arel::Attributes::Attribute#eql? performs value-based comparison (name + relation) without going through the ArelExtensions override.

# Before
if join_root.left == pk
# After
if join_root.left.eql?(pk)

Verification

pk  = User.arel_table[:id]
pk2 = User.arel_table[:id]

pk.equal?(pk2)  # => false (different objects)
pk.eql?(pk2)    # => true  (same name + relation)
pk == pk2       # => Arel::Nodes::Equality (always truthy — the bug)