Fix "Get Changes" step in workflow

[trs]

The "Get Changes" step should use git log to list all the commits between the last tag and the new tag so that the Github release description body lists those changes.

This isn't working though and just gives errors like: fatal: Not a valid object name v0.4.8^.
Running the command locally does seem to work though 😕

Example run: https://github.com/trs/shift-code/runs/3863540271?check_suite_focus=true