The problem was the directory structure. Locating the source files in a src
sub-directory resolved the issue.
my_module/
+---LICENCE.md
+---pyproject.toml
+---README.md
+---requirements.txt
+---src/
| +---my_module/
| +---__init__.py
| +---my_module.py
| +---my_module.tcss
+---git/