Ensure GFile is unreferenced to avoid filename memory leak

[lovell]

Hello @federicomenaquintero, thank you very much for all the time you continue to devote to librsvg.

v2.40.20 appears to have introduced a small memory leak of the filename that I think was via the change in commit 475764f

The change in this PR should ensure the GFile instance is unreferenced for all paths.

(The Gnome GitLab instance won't let me register - "Email is not from an allowed domain" - hence the use of GitHub.)

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[federicomenaquintero]

Thanks for noticing this! I'll review this on Monday. Please ignore the auto-closing bot - GNOME's gihub mirror is configured to disallow pull requests, but I'm happy to look at them.

(If you want to send a pull request in the future, we have https://gitlab.gnome.org/GNOME/librsvg - you can create an account there and have a similar workflow to here.)

[lovell]

@federicomenaquintero Thank you.

I've now been able to register with gitlab.gnome.org using a gmail.com address so I guess there are restrictions in place. Given I was able to change to a non-gmail address as soon as I was registered suggests those restrictions could probably be removed.

I'll open a merge request there now.

[lovell]

Moved to https://gitlab.gnome.org/GNOME/librsvg/merge_requests/2