Backport: Template and template parts updated labels

[ntsekouras]

Trac ticket: https://core.trac.wordpress.org/ticket/61095#ticket

In this Gutenberg PR: WordPress/gutenberg#61146 we added the item_updated label to template and template parts labels. We need to back port this for the next release.

If you save/update a template in post editor right now, the notification message renders post updated. You can test this only with templates right now, since the editing of template parts in isolation in post editor will be available in the next release.

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[ellatrix]

Thanks @ntsekouras!

[audrasjb]

Approved for core merge, thanks 👍

[ntsekouras]

Merged to Core in https://core.trac.wordpress.org/changeset/58055

Thank you!