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Merge pull request #16508 from jbsmith86/master

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create_table + transactional_fixtures = :bomb:
Use the method for determining attribute methods rather than duplicating

I've been trying to reduce the number of places that care about
`attributes`, and its existence. We have a method for this check, let's
use it instead.
Merge pull request #16505 from sgrif/sg-attribute-internals

Use the method for determining attribute methods rather than duplicating
prefer `has_attribute?` over `attributes.key?`.

Follow up to the discussion on #16505.
fix typo in method name (broken build :sweat:)
Fixed link for in_place_editor [ci skip]

closes #16512
Point to rubygems instead of Rails GitHub. [ci skip]

The rails repository is not the official plugin anymore