Hint text for a character count is included by screen readers as part of the count message

[36degrees]

Description of the issue

If a character count also has a hint associated with the textarea, some screen readers also include the hint text whenever the count message is announced.

Steps to reproduce the issue

1. Go to https://govuk-frontend-review.herokuapp.com/components/character-count/with-hint/preview
2. Focus the textarea and wait for the accessible name, type and description to be read
3. Enter characters in the text area

Actual vs expected behaviour

Expected: Only the count message should be announced, for example "You have 9 characters remaining."

Actual: The hint text is also announced in:

• JAWS 2021.2103.174 / Chrome 96
• JAWS 2021.2103.174 / Firefox 95
• NVDA 2021.2 / Chrome 96
• NVDA 2021.2 / Firefox 94

"You have 5 characters remaining. Don't include personal or financial information, eg your National Insurance Number or credit card details."

This hint text was also announced very occasionally in VoiceOver / Safari 15.2 (macOS Big Sur) with no discernible pattern.

JAWS 2021.2103.174 / IE11 and VoiceOver / Safari (iOS 15.2) behave as expected, announcing only the remaining count.

Environment (where applicable)

• Operating system: As above
• Browser: As above
• Browser version: As above
• GOV.UK Frontend Version: v4.0.0

[36degrees]

I believe this is likely because changes to the accessible description are announced a little like live regions (the character count message is associated with the textarea using aria-describedby).

See also https://www.davidmacd.com/blog/test-aria-describedby-errormessage-aria-live.html

Some overlap with #2485.