Allow #algolia_dirty? to be defined privately

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Q	A
Bug fix?	no
New feature?	no
BC breaks?	no
Related Issue	n/a
Need Doc update	no

Describe your change

Include all methods when determining whether an object responds to #algolia_dirty?.

What problem is this fixing?

Object#send can be used to call both public and private methods, but Object#respond_to? only returns true if the argument is a public method. This inconsistency is confusing.

To be more consistent, either #send should be replaced with #public_send, or #respond_to should have its optional include_all argument set to true (in this PR I opted for the latter).

There are many other places in the code that check if a method is defined publicly before calling it via send (checking if callbacks methods like after_commit, etc are defined). I can update those as well if wanted. But #algolia_dirty? seemed like the most critical, since that's the one end users would define themselves (rather than have defined by the framework they're using).

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(CI failures are all caused by Cannot add API key for app ID NOCTT5TZUU: Algolia API error [403] Invalid Application-ID or API key)