Fix filename of fix-macosvfs-file-sharing.png

[Flowdalic]

Downstream bug: https://bugs.gentoo.org/946689

It seems like bulding the documentation is not part of the CI yet (see also #7383). If so, maybe you should consider adding it.

[mgallien]

@Flowdalic building the documentation is part of the CI but currently only via a private drone instance that cannot for security reasons be run for community contributed PRs.
thanks for the PR
I will review it

[mgallien]

@Flowdalic just for your info
I created #7708 to fix the CI to provide proper feedback on doc build errors for PR

[mgallien]

/backport to stable-3.15

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