Disable maintenance mode - fix broken Ruby command

What does this MR do?

The current Ruby command to disable maintenance mode does not work:

irb(main):013:0> ::Gitlab::CurrentSettings.update_attributes!(maintenance_mode: false)
Traceback (most recent call last):
        2: from (irb):13
        1: from lib/gitlab/current_settings.rb:32:in `method_missing'
NoMethodError (undefined method `update_attributes!' for #<ApplicationSetting:0x00007fbcc6e99938>)
Did you mean?  update_attribute

I tried various combinations:

irb(main):014:0> ::Gitlab::CurrentSettings.update_attribute!(maintenance_mode: false)
Traceback (most recent call last):
        3: from (irb):13
        2: from (irb):14:in `rescue in irb_binding'
        1: from lib/gitlab/current_settings.rb:32:in `method_missing'
NoMethodError (undefined method `update_attribute!' for #<ApplicationSetting:0x00007fbcc5286fe8>)
Did you mean?  update_attribute
irb(main):015:0> ::Gitlab::CurrentSettings.update_attribute(maintenance_mode: false)
Traceback (most recent call last):
        3: from (irb):14
        2: from (irb):15:in `rescue in irb_binding'
        1: from lib/gitlab/current_settings.rb:32:in `method_missing'
ArgumentError (wrong number of arguments (given 1, expected 2))
irb(main):016:0> ::Gitlab::CurrentSettings.update_attribute('maintenance_mode', false)
=> true

While ::Gitlab::CurrentSettings.update_attribute('maintenance_mode', false) works - I think it makes more sense to use ::Gitlab::CurrentSettings.update!(maintenance_mode: false) instead, since the Ruby command is similar to how you would enable maintenance mode.

This of course works:

irb(main):012:0> ::Gitlab::CurrentSettings.update!(maintenance_mode: false)
=> true

Related issues

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