Update to serde_yaml 0.9.*

The update to serde_yaml 0.9 slightly changes the format of the layout-files. It is necessary to change all occurences of set_view: and locking:, to !set_view and !locking, respectively. Fixed by adding #[serde(with = "serde_yaml::with::singleton_map", default)] in the appropriate place; see link 1 and link 2 for more information about this.

I tested this change on my PinePhone, and it seemed to work normally.

Fixes #379 (closed)

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Note: serde_yaml 0.9 is not available in Debian Trixie yet; so the build_deb-CI-pipeline cannot be successfully completed yet.