Restrict importlib-metadata version

Twine isn't compatible with importlib-metadata 8 released yesterday.

Twine issue: https://github.com/pypa/twine/issues/977

Part of iwoca/devops/support#290

wheel_push.yml

@@ -23,7 +23,7 @@
 
   image: public.ecr.aws/docker/library/python:${PYTHON_VERSION}
   script:
-    - pip install twine==4.0.2 build==0.9.0
+    - pip install twine==4.0.2 build==0.9.0 "importlib-metadata<8"
     - python -m build .
     - twine upload --repository-url http://pypi.iwoca.co.uk dist/* -u pypi -p ${PYPI_USER_PASSWORD}
   artifacts: