[Merged by Bors] - Fix bug that prevents deserializing stacks and demos using serde_yaml 0.9

[sbernauer]

Description

With serde_yaml 0.9 a bug was introduced that stopped us from parsing stacks and demos.

cargo r -- demo list 
    Finished dev [unoptimized + debuginfo] target(s) in 0.05s
     Running `target/debug/stackablectl demo list`
[WARN ] Failed to parse demo list from https://raw.githubusercontent.com/stackabletech/stackablectl/main/demos/demos-v1.yaml: demos.trino-taxi-data.manifests[0]: invalid type: map, expected a YAML tag starting with '!' at line 14 column 9

This PR fixes this

Review Checklist

• [ ] Code contains useful comments
• [ ] (Integration-)Test cases added (or not applicable)
• [ ] Documentation added (or not applicable)
• [ ] Changelog updated (or not applicable)
• [ ] Cargo.toml only contains references to git tags (not specific commits or branches)

Once the review is done, comment bors r+ (or bors merge) to merge. Further information

[sbernauer]

bors r+

[bors[bot]]

Pull request successfully merged into main.

Build succeeded:

• Run Rustfmt