Fix diff-poetry-lock check

[colindean]

diff-poetry-lock check broke without change so there must be a runtime dependency on something. Looking at this failure, it looks like it's using Poetry and perhaps the Poetry 2.0 release broke an assumption.

[colindean]

See nborrmann/diff-poetry-lock#15 for the fix, but @nborrmann seems to be inactive on GitHub for several months.

[colindean]

I'm going to have an internal-to-Target discussion about whether or not to fork or rewrite diff-poetry-lock, with some knobs around permanency and maintainership.