[#7194] Tweak wording on Internal Review mailer

[mdeuk]

Relevant issue(s)

Fixes #7194

What does this do?

This improves the internal review mailer template, by removing the slightly cliché and dated reference to -"the Internet"_, replacing with the more common phrasology "available online".

Why was this needed?

We should be aiming to make our services as accessible as possible - and part of that involves making sure we're using plain language. The template is a 'starter for ten' for users - we expect them to customise it, but getting the basics down to a simple format will aid comprehension.

Implementation notes

Nothing of note.

Screenshots

N/A

Notes to reviewer

I've updated the specs, to the best of my knowledge.

[mdeuk]

Spec fails 😔:

rspec ./spec/models/outgoing_message_spec.rb:1931 # OutgoingMessage when making an outgoing message should produce the expected text for an internal review request
rspec ./spec/models/outgoing_message_spec.rb:778 # OutgoingMessage#get_default_message an internal_review produces the expected text for an internal review request
rspec ./spec/models/outgoing_message_spec.rb:584 # OutgoingMessage#body validation when it's an internal review includes a all correspondence being available online
rspec ./spec/models/outgoing_message/template/internal_review_spec.rb:34 # OutgoingMessage::Template::InternalReview#body returns the expected template text
rspec ./spec/models/outgoing_message/template/internal_review_spec.rb:81 # OutgoingMessage::Template::InternalReview#letter returns the letter