Fix warning about LOGGER.warn()

[terriko]

We're getting the following warning:

test/test_cli.py::TestCLI::test_console_output_depending_reportlab_existence
  D:\a\cve-bin-tool\cve-bin-tool\cve_bin_tool\output_engine\__init__.py:318: DeprecationWarning: The 'warn' method is deprecated, use 'warning' instead
    LOGGER.warn("PDF output requires install of reportlab")

Should just change that line to be LOGGER.warning(...) and it should be resolved.

(No hurry on fixing this one, so experienced contributors, please leave this bug for someone who's looking for their first or second commit.)

[M-Faheem-Khan]

Hi, can I take this issue?

[terriko]

Feel free!

[M-Faheem-Khan]

Thanks! :)