Add github actions testing

[skjnldsv]

Add testing

@rullzer I feel like adding those here doesn't really defined themselves as the 'standard actions' files :)

Maybe we should have a repo for it?

[skjnldsv]

I give up, somehow the connexion is ok, because the nextcloud setup is working properly for the first part.
But Nextcloud always create its own admin db user, and once it creates it (oc_admin, it works) it can't connect with it afterwards.

[skjnldsv]

So, now that server is fixed nextcloud/server#19303
I can move on :)

Ideally since github actions doesn't support services.if, but only steps.if, I cannot start services based on what db matrix is being used. So we'd need to split things in the meantime :/

There are a few steps actions like https://github.com/Harmon758/postgresql-action & https://github.com/mirromutth/mysql-action but it seems to have a few bugs (mysql) or missing features (port setting pgsql)

[skjnldsv]

/compile amend /