Add github action to publish package to testPyPI

.github/workflows/pypi.yml

@@ -0,0 +1,22 @@
+name: PyPI publishing
+
+on: push
+
+jobs:
+  pypi:
+    runs-on: ubuntu-latest
+    environment: release
+    permissions:
+      id-token: write
+    steps:
+      - uses: actions/checkout@v4
+      # build the calculate-liam package and store outputs in dist folder
+      - run: pipx run build calculate-liam -o dist
+      # check the files in dist are valid
+      - run: pipx run twine check dist/*
+      # if this commit is tagged, upload the release to (test)PyPI
+      - if: github.event_name == 'push' && startsWith(github.event.ref, 'refs/tags/')
+        uses: pypa/gh-action-pypi-publish@release/v1
+        with:
+          repository-url: https://test.pypi.org/legacy/
+          verbose: true