check version before changelog

[RensDimmendaal]

Note: I've removed python 3.9 from the testing matrix as it threw an error that fastcore requires >=3.10.

After this PR running nbdev_release_gh will check if the version has been bumped.
This will avoid the annoying issue of having a duplicate version number in the changelog and committing this accidentally.

Here's what it looks like when you get the error:

$ nbdev_release_gh
Error: Version bump required: expected: >0.0.3, got: 0.0.3.

[jph00]

Thanks @RensDimmendaal :)