Ignore fsync errors

[MichaelEischer]

What is the purpose of this change? What does it change?

Storing a repository on a filesystem that does not support fsync is currently not possible. This PR syncs the ignored fsync errors from the restic backend to also allow storing a repository on these filesystems. However, this is not recommended as without fsync it is not possible to guarantee the integrity of uploaded data.

In addition, macOS Ventura seems to have introduced an additional error code, see #198.

Was the change discussed in an issue or in the forum before?

Fixes #198.

Checklist

• [x] I have enabled maintainer edits for this PR
• [ ] I have added tests for all changes in this PR
• [x] I have added documentation for the changes (in the manual)
• [ ] There's a new file in changelog/unreleased/ that describes the changes for our users (template here)
• [x] I have run gofmt on the code in all commits
• [x] All commit messages are formatted in the same style as the other commits in the repo
• [ ] I'm done, this Pull Request is ready for review

[MichaelEischer]

I've replaced the implementation in the PR with the changes made for restic in https://github.com/restic/restic/pull/4021 . The fsync handling is now largely copy & paste from restic, which should make it easier to maintain this error handling mess.

[bdillahu]

For what it's worth, it works for me as I was having the errors.