Fix wrong timezone in schedule XML

[asdil12]

This just contains the proposed fix from https://github.com/openSUSE/osem/issues/3242#issuecomment-1565428268

I have no idea if it actually works (the comments says that it was tested at least) because the docker deployment described in the README doesn't work.

I guess if it doesn't introduce a syntax error, it can't get more broken so we can as well merge it.

Fixes #3242 Fixes #3417

Checklist

• [ ] I have read the Contribution & Best practices Guide.
• [ ] My branch is up-to-date with the upstream master branch.
• [ ] The tests pass locally with my changes.
• [ ] I have added tests that prove my fix is effective or that my feature works(if appropriate).
• [ ] I have added necessary documentation (if appropriate).

Short description of what this resolves/which issues does this fix?:

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Changes proposed in this pull request:

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