Template Translation are not included in the gettext_compact domain

[Blendify]

Describe the bug
With a project that has custom templates with translatable messages these messages are not added to the gettext domain specified with gettext_compact. This causes issues with translation management websites that expect all messages to be in one translation file. For example weblate.

To Reproduce
Steps to reproduce the behavior:

make gettext message files for a project that overrides the default templates with translatable messages.

Expected behavior
The gettext builder should generate one message file and not output sphinx.po when gettext_compact specifies a custom domain.

Your project
https://svn.blender.org/svnroot/bf-manual/trunk/blender_docs/

Environment info

• OS: Ubuntu 20.10
• Python versin: 3.8.6
• Sphinx version: 3.5.2
• Sphinx extensions: sphinx-intl

Additional context

https://docs.weblate.org/en/latest/devel/integration.html#project-and-component-structure