fix syntax in publish.yml

Documenting debug process

This stackoverflow answer suggested pyyaml as a package that would help the developer check, within the local environment, that a yaml file is valid.

To run it on Windows where the < symbol might not be recognised, do this:

run poetry add pyyaml (or pip install pyyaml to install the package)
Create an empty python file with the code below, and run it. Remember to write the file path as a string.
```
import yaml 
print(yaml.safe_load("write_path_to_yaml_file_here")) 
```
If an error is returned, then the file is not properly formatted.

data-to-insight / csc-validator-be-903

fix syntax in publish.yml #786