🐛Ensure the default `$PATH` value is pre-loaded

This patch imports the system-global profile script to
populate the `$PATH` variable with the typically available binary
paths.

Ref:
https://github.com/pypa/gh-action-pypi-publish/issues/112#issuecomment-1340065840

.github/workflows/self-smoke-test-action.yml

@@ -84,6 +84,8 @@ jobs:
           }}/public/
     - name: ✅ Smoke-test the locally checked out action
       uses: ./test
+      env:
+        PATH: utter-nonsense
       with:
         user: ${{ env.devpi-username }}
         password: ${{ env.devpi-password }}

twine-upload.sh

@@ -5,6 +5,7 @@ set -Eeuo pipefail
 # NOTE: These variables are needed to combat GitHub passing broken env vars
 # NOTE: from the runner VM host runtime.
 # Ref: https://github.com/pypa/gh-action-pypi-publish/issues/112
+. /etc/profile  # Makes python and other executables findable
 export PATH="$(python -m site --user-base)/bin:${PATH}"
 export PYTHONPATH="$(python -m site --user-site):${PYTHONPATH}"