Bump subvertpy to 0.11 in dev-requirements.txt
Bump subvertpy to 0.11 in dev-requirements.txt

subvertpy finally did a release, which includes support for modern
Python 3.x. This change bumps our dependency to pull that in.

Testing Done:
Installed subvertpy 0.11 and saw that all unit tests passed on
Python 3.10.

Reviewed at https://reviews.reviewboard.org/r/12085/

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