Local GNU gettext template (message.pot_t) not used

[bandali]

Describe the bug

Sphinx does not use the copy of message.pot_t in the project's _templates directory.

How to Reproduce

$ git clone https://review.jami.net/jami-docs
$ cd jami-docs
$ git fetch https://review.jami.net/jami-docs refs/changes/27/22427/7 && git checkout FETCH_HEAD
$ pip install -U sphinx sphinx-rtd-theme myst_parser
$ make gettext
$ head _build/gettext/index.pot

Notice that the file was created using the message.pot_t template shipped with Sphinx itself, rather than the copy in _templates/message.pot_t.

Expected behavior

Sphinx should use the _templates/message.pot_t file from the project repository as the template for creating the pot files when running make gettext.

Your project

https://review.jami.net/c/jami-docs/+/22427

Screenshots

No response

OS

Trisquel 10 GNU/Linux (based on Ubuntu 20.04)

Python version

3.8.10

Sphinx version

5.1.1

Sphinx extensions

myst_parser, sphinx.ext.autosectionlabel, sphinx.ext.extlinks, sphinx_rtd_theme

Extra tools

No response

Additional context

No response