i18n: toggle-header is not captured in po-file for translation

[fish-train]

Describe the problem

toggle-header is not captured in po file for translation.

Steps to reproduce

1. Input toggle-header:

.. toggle-header::
    :header: Example 1 **Show/Hide Code**

        Content for header

2. Translate with sphinx-intl

Results

msgid Example 1 **Show/Hide Code** is not captured in po file for translation,