build(python): add support for Python 3.13 (#732)

[jlemesh]

Closes reanahub/reana#837

Add support for Python 3.13.

Replaced cgi.parse_headers with email.message.Message as recommended in https://peps.python.org/pep-0594/#cgi. Added test to make sure it does the same things that the previous code did. Also tested as in #490.

[jlemesh]

3.13 tests fail with:

reana_client/api/client.py:10: in <module>
    import cgi
E   ModuleNotFoundError: No module named 'cgi'

CGI module is "Deprecated since version 3.11, will be removed in version 3.13": https://docs.python.org/3/library/cgi.html

[tiborsimko]

3.13 tests fail with:

We use cgi in one place only:

$ git grep cgi
reana_client/api/client.py:10: import cgi
reana_client/api/client.py:504:            value, params = cgi.parse_header(content_disposition)

Can you look at updating that part of the code?

[tiborsimko]

Nice tests 👍