fix: set package.json version from release please

[lukekarrys]

No description provided.

[wraithgar]

What bug is this fixing and how easy would it be to test?

[lukekarrys]

Currently when run with workspaces, release-please is not bumping package.json#version (npm/cli@683973c). This is a regression from #183 and puts the tree into an invalid state so npm i will fail.

It's not easy to test without mocking a bunch of stuff due to how release-please itself it setup. This class extends a release-please class which makes a lot of assumptions about data structures. Originally I avoided testing since it was mostly mocks, but this bug points to us needing tests here so mocks might be ok in this case.

[lukekarrys]

Ended up adding a test for it with some mocked release-please data structures. It will give us more confidence in the future as we keep up with release-please updates that this is still working.