I18N string fixes for 7.2

[joedolson]

This ticket is for any string improvements that do not directly relate to specific tickets.

Previously:

• #64899 (7.1)
• #64244 (7.0)
• #63629 (6.9)

This PR adds missing translator comments for translatable strings that include a trailing space after the colon, as part of the WordPress 7.1 I18N string improvements.

### Changes

• Added translator comment for the_tags() default prefix (Tags: ) in category-template.php.
• Added translator comments for trackback/pingback moderation email labels (Trackback excerpt: and Pingback excerpt: ) in wp_notify_moderator() within pluggable.php.

These follow the established pattern used in WP_PHPMailer (/* translators: There is a space after the colon. */) so translation tooling (WP-CLI i18n make-pot, Poedit) correctly preserves the trailing space for translators.

Trac ticket: https://core.trac.wordpress.org/ticket/65815

## Use of AI Tools

N/A

Thanks for the PR! Merged in r63030.

The $domain parameter of __(), _e(), _x() and the other translation functions already defaults to default. Passing 'default' explicitly in core files is redundant, and core convention is to omit the argument entirely.

Trac ticket: https://core.trac.wordpress.org/ticket/65815