Update INSTALL docs for Qubes (Fedora 40 → Fedora 41)

[deeplow]

What happened?

INSTALL.md mentions Fedora 40. Even though it hasn't reached its end of life, the Fedora 41 template has already been out for a while. So it should be bumped before then.

Timing-wise, perhaps it makes sense to bump it just after Qubes 4.2.4 is released (it's currently in release candidate stage). This is just the Qubes 4.2 ISO with all the latest updates and importantly here a Fedora 41 template instead of Fedora 40. This will mean that new installs won't have Fedora 40 available.

Linux distribution

Qubes 4.2

Dangerzone version

0.8.1

Podman info

(not relevant)

Document conversion logs

(not relevant)

Additional info

No response

[apyrgio]

Adding it to the 0.9.0 milstone then, so that we can bump the Fedora version and test it, before putting out a new release.