Crash on Chrome Accept header with v=b3 parameter

[snarfed]

negotiator currently crashes on a v=b3 parameter that Chrome added to its Accept header a while ago. Here's the full string:

text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.9

Stack trace:

ValueError: could not convert string to float: 'b3'
  at ._interpret_accept_field ( /layers/google.python.pip/pip/lib/python3.9/site-packages/negotiator/negotiator.py:652 )
  at ._analyse_accept ( /layers/google.python.pip/pip/lib/python3.9/site-packages/negotiator/negotiator.py:557 )
  at .negotiate ( /layers/google.python.pip/pip/lib/python3.9/site-packages/negotiator/negotiator.py:423 )

Related:

• https://web.dev/signed-exchanges/#web-packager-cli
• chrome request header "application/signed-exchange;v=b3" causing mime parse error emicklei/go-restful#400
• chrome request header "application/signed-exchange;v=b3;q=0.9" causing Registry render error RDFLib/pyLDAPI#21
• RDFLib/pyLDAPI@8ac446e