Removing all caps for ERROR messages

[man4toman]

Removing all caps for ERROR messages, from core's Trac:
​Remove 'Error:' prefixes from error notices

Cc: @imath

[imath]

Hi @man4toman

Thanks for your feedback and for the reference to the Core trac ticket. Let’s do it in our next major release 👌.

Patch looks good to me, if a member of the team is faster than me, don’t hesitate to commit it.

[imath]

In 12657:

A11y: Use sentence case for the word Error in some error messages

Using all caps should be avoided for better readability and because screen readers may pronounce all-caps words as abbreviations.

Props man4toman

Fixes #8300