Update notification categories screenshot

[HennaAbbas]

Update the email categories screenshot to show the latest notification
filter options in the CircleCI UI, including the "On default branch
(failed, error, unauthorized)" filter option.

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Description

What did you change?

• Replaced the email-categories.png screenshot with an updated version
  showing the current notification filter UI
• Added the missing "On default branch (failed, error, unauthorized)"
  filter option to the documentation text
• Resized the new screenshot to 915px x 825px to maintain consistency
  with the original image dimensions

Reasons

Why did you make these changes? What problem does this solve?

The existing screenshot was outdated and did not accurately reflect the
current CircleCI notification settings interface. This update ensures
users see an accurate representation of the notification filter options
available to them. The documentation text was also missing the "On
default branch (failed, error, unauthorized)" filter option that exists
in the UI, creating a mismatch between the docs and the actual product.

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