Clarify allow_deprecated_singular_associations_name deprecation warning

[jonathanhefner]

Follow-up to #45344.

Currently, when allow_deprecated_singular_associations_name is true, a deprecation warning like the following is displayed:

> Comment.belongs_to :post
> Comment.where(posts: 1).count
DEPRECATION WARNING: In Rails 7.2, referring to singular associations by their plural name will be deprecated.
To continue querying `post` use `posts` instead.
You can get the new more performant behavior now by setting config.active_record.allow_deprecated_singular_associations_name = false

The warning advises "use posts instead", but the user's code should actually use post, i.e. Comment.where(post: 1).count. The mismatch is likely due to the level at which the deprecation warning is emitted. associated_with? does indeed expect table_name to be posts, but where expects post.

This commit changes the deprecation warning to avoid advising a specific usage, but still be explicit about what is wrong:

> Comment.where(posts: 1).count
DEPRECATION WARNING: Referring to a singular association (e.g. `post`) by its plural name (e.g. `posts`) is deprecated.

To convert this deprecation warning to an error and enable more performant behavior, set config.active_record.allow_deprecated_singular_associations_name = false.

[byroot]

LGTM. I cc-ed @HParker just in case.

[HParker]

Great catch thank you! 🙇
Reflection name should actually be more correct in more cases too like when the reflection and table name do not match. I like this change a lot 👍

[HParker]

Should the reflection.plural_name here be the table name since that is what they passed in?

I am worried about a case where you pass in the plural table name and we instead say you can't pass the plural reflection name which seems confusing.

[HParker]

Ah, I think if you did that and we found the reflection from the singular name, it should be the same unless it is a inflection difference, which I don't think we should need to worry about here.