Upload py7zr 0.21.0+dfsg-2 to fix test code

[yokota]

Hello Python team,

I was pushed fixes to salsa.
It enables some more test code in py7zr.
Please upload py7zr 0.21.0+dfsg-2 to Debian.

https://salsa.debian.org/python-team/packages/py7zr

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YOKOTA Hiroshi