core/config: resolve MY_CONFIG path before warning unrelatedness

[yutotakano]

PR #336 added a warning for when the detected my.config module is not in a subpath of MY_CONFIG. This was to help diagnose bad setups.

This warning is currently faulty. Because the paths aren't resolved before comparison, setting MY_CONFIG to a relative value like ./config will fail the check despite the config module existing within the current working directory. (Using relative values for the env might be seen with a directory-sandboxed HPI setup, using something like direnv)

Expected my.config to be located at ./config, but instead its path is <someabsolutepath>\config\my\config\__init__.py.
This will likely cause issues down the line -- double check ./config structure.

The pull request resolves both paths used in the comparison to the absolute path. The problem described above is fixed, which I verified with a locally editable install.