use xdg-config for MangoHud config

[Mershl]

xdg-config provides an generic approach that allows users and distros to use a config dir other than ~/.config

tested on Fedora 40/41/42

fixes #429

[flathubbot]

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[Mershl]

The manifest validation throws an https://docs.flathub.org/docs/for-app-authors/linter#finish-args-unnecessary-xdg-config-subdir-mode-access, but that's exactly what we want here.

[victorsouzaleal]

The manifest validation throws an https://docs.flathub.org/docs/for-app-authors/linter#finish-args-unnecessary-xdg-config-subdir-mode-access, but that's exactly what we want here.

It's because the :ro in this case with xdg-config is really unnecessary, it works as expected with xdg-config/MangoHud, I didn't want to open another PR because you already reported the issue and opened a PR, try to fix it.

[Mershl]

It's because the :ro in this case with xdg-config is really unnecessary

Omitting :ro will default to read AND write permission, which is best practice to avoid for these cases. But if this infact avoids the validation error then... I'll force push the PR in a sec.

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[Mershl]

The manifest validation throws an https://docs.flathub.org/docs/for-app-authors/linter#finish-args-unnecessary-xdg-config-subdir-mode-access, but that's exactly what we want here.

It's because the :ro in this case with xdg-config is really unnecessary, it works as expected with xdg-config/MangoHud, I didn't want to open another PR because you already reported the issue and opened a PR, try to fix it.

xdg-config/MangoHud throws the same validation error, see log above. I'm reverting it back to :ro again.

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[RayJW]

This won't build unless there is an exception added to https://github.com/flathub-infra/flatpak-builder-lint. A PR will probably be accepted pretty easily, seeing as the permission is already present, just differently and the need for it is justified.