🔧 Add publishing GH action (#20)

Author: chrisjsewell

.github/workflows/ci.yaml

@@ -2,6 +2,8 @@ name: CI
 on:
   push:
     branches: [main]
+    tags:
+      - "v[0-9]+.[0-9]+.[0-9]+*"
   pull_request:
 jobs:
 
@@ -67,3 +69,27 @@ jobs:
       uses: re-actors/alls-green@release/v1
       with:
         jobs: ${{ toJSON(needs) }}
+
+  publish:
+
+    name: Publish to PyPi
+    needs:
+    - check
+    if: github.event_name == 'push' && startsWith(github.event.ref, 'refs/tags')
+    runs-on: ubuntu-latest
+    steps:
+    - name: Checkout source
+      uses: actions/checkout@v4
+    - name: Set up Python 3.10
+      uses: actions/setup-python@v5
+      with:
+        python-version: "3.10"
+    - name: install flit
+      run: |
+        pip install flit~=3.4
+    - name: Build and publish
+      run: |
+        flit publish
+      env:
+        FLIT_USERNAME: __token__
+        FLIT_PASSWORD: ${{ secrets.PYPI }}