fix(datetime): next and previous buttons have correct labels

[liamdebeasi]

Pull request checklist

Please check if your PR fulfills the following requirements:

• Tests for the changes have been added (for bug fixes / features)
• Docs have been reviewed and added / updated if needed (for bug fixes / features)
  • Some docs updates need to be made in the ionic-docs repo, in a separate PR. See the contributing guide for details.
• Build (npm run build) was run locally and any changes were pushed
• Lint (npm run lint) has passed locally and any fixes were made for failures

Pull request type

Please check the type of change your PR introduces:

• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes
• Other (please describe):

What is the current behavior?

Issue URL: resolves #25844

What is the new behavior?

• Narrators no longer read the icon aria-label. Instead, they read the custom "previous month" or "next month" labels we have assigned to the buttons.

Does this introduce a breaking change?

• Yes
• No

Other information

[iamandersonp]

This fix will add the correct aria-labels but only for a english screen reader, if you have multilingual aplication it wont translate. The months and the days in calendar are translated via locale (or at least with the locale the screen reader says the days and monts in correct language)

[liamdebeasi]

That capability is not built into ion-datetime. If you would like to see support for that added I recommend opening a Feature Request.