Bug Fix of #3434 : Incorrect Argument Type in write_params_file()

When running the command nf-core pipelines create-params-file, an AttributeError was raised because the write_params_file() method of ParamsFileBuilder expected its first argument to be a Path object. However, a string representing the output parameter file name was passed instead, causing the error.
This fix ensures that the argument is properly converted to a Path object before being passed to write_params_file(), resolving the issue.

PR checklist

• This comment contains a description of changes (with reason)
• CHANGELOG.md is updated
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• Documentation in docs is updated