gettext: Replace all usage of "elementary/actions/gettext-template@next" to "elementary/actions/gettext-template@main"

### Problem

We have some repositories that uses `elementary/actions/gettext-template@next` but this branch is old causes a build error like this:

https://github.com/elementary/panel-sound/actions/runs/32421827309/job/96595301394

```
[007](https://github.com/elementary/panel-sound/actions/runs/32421827309/job/96595301394#step:6:2008)
Processing triggers for desktop-file-utils (0.26-1ubuntu3) ...
Processing triggers for hicolor-icon-theme (0.17-2) ...
Processing triggers for libc-bin (2.35-0ubuntu3.14) ...
Processing triggers for dbus (1.12.20-2ubuntu4.1) ...
Processing triggers for bamfdaemon (0.5.6+22.04.20220217-0ubuntu1) ...
Rebuilding /usr/share/applications/bamf-2.index...
Processing triggers for ca-certificates (20260601~22.04.1) ...
Updating certificates in /etc/ssl/certs...
0 added, 0 removed; done.
Running hooks in /etc/ca-certificates/update.d...
done.
Processing triggers for libgdk-pixbuf-2.0-0:amd64 (2.42.8+dfsg-1ubuntu0.5) ...
E: Unable to correct problems, you have held broken packages.
```

### Proposal

Replace all usage of `elementary/actions/gettext-template@next` to `elementary/actions/gettext-template@main`:

https://github.com/search?q=org%3Aelementary+elementary%2Factions%2Fgettext-template%40next&type=code

### Prior Art (Optional)

https://github.com/elementary/panel-sound/commit/200db283cf6568335a35d1f69edb930964a2cc23