The current implementation checks if `auto_notify` is an instance of
`TrueClass` or `FalseClass` (in that order). As this is a "hot path" as
far as Bugsnag is concerned (runs on all notifications), we can consider
applying the following optimizations:

- `true` and `false` are singleton instances of `TrueClass` and
  `FalseClass`, respectively. Therefore, we can rely on the slightly
  faster `.equal?` check, which relies on object identity.
- `false` is the default for the method, so is likely the most common
  usage, so we can invert the order of the check and check for `false`
  before `true`, to benefit from short circuiting in the more common case.

This new implementation is faster in the `false` and non-boolean cases,
and while it is slower in the `true` case (because of the order
inversion), it is still faster than the previous approach was in the
`false` case.

We can test this using the following benchmark:

    require "benchmark/ips"
    [
      false, # Default    – Probably most common case
      true,  # Override   – Probably accounts for almost all other usage
      {},    # Deprecated – Probably barely any usage
    ].freeze.each do |auto_notify|
      Benchmark.ips do |x|
        x.compare!
        x.report("#{auto_notify}.is_a? TrueClass or #{auto_notify}.is_a? FalseClass (status quo)") do
          auto_notify.is_a? TrueClass or auto_notify.is_a? FalseClass
        end
        x.report("false.equal? #{auto_notify} or true.equal? #{auto_notify}         (proposed)  ") do
          false.equal? auto_notify or true.equal? auto_notify
        end
      end
    end

which produces the following results:

    Implementation                                                              |`false`             |`true`              |`{}`
    ----------------------------------------------------------------------------|--------------------|--------------------|--------------------
    `auto_notify.is_a? TrueClass or auto_notify.is_a? FalseClass` _(status quo)_|11.978M (± 0.6%) i/s|17.122M (± 1.3%) i/s|11.814M (± 0.5%) i/s
    `false.equal? auto_notify or true.equal? auto_notify`         _(proposal)_  |17.955M (± 0.4%) i/s|13.553M (± 1.6%) i/s|13.420M (± 2.5%) i/s