[webencodings] Update to 0.6.*

[donbarbos]

Closes: #16212
Diff: CourtBouillon/webencodings@v0.5.1...v0.6.1

[github-actions]

According to mypy_primer, this change has no effect on the checked open source code. 🤖🎉

[donbarbos]

The library passes a string as the mapping argument to codecs.charmap_encode/decode functions, but this isn't currently listed as an accepted input type in typeshed. Would it make sense to add it?
small demo:

import codecs
user_decoding_table = ''.join(chr(c if c < 128 else c + 0xF700) for c in range(256))
codecs.charmap_decode(b'some bytes', None, user_decoding_table)