newline character in requirements parser

[paulmaxus]

Issue related to #3935:
panel==1.2.0

When using panel convert with the --requirements option and a requirements.txt file, I receive this error:
Failed to convert file to pyodide-worker target: Requirements parser raised following error: Expected end or semicolon (after version specifier)

The issue is that the newline character is specified as '/n' when splitting the text, even though it's '\n'.

I would suggest something like this to avoid the newline character entirely:

requirements_path = pathlib.Path(requirements)
with requirements_path.open(encoding='utf-8') as f:
    requirements = f.read().splitlines()