fix: install twine in publish jobs

- Add 'pip install twine' step to both TestPyPI and PyPI publish jobs
- Fixes 'twine: command not found' error
- Required for uploading packages to PyPI

Author: BenjaminWatts

.github/workflows/publish.yml

@@ -58,6 +58,9 @@ jobs:
         name: python-package-distributions
         path: dist/
 
+    - name: Install twine
+      run: pip install twine
+    
     - name: Publish to TestPyPI
       env:
         TWINE_USERNAME: __token__
@@ -81,6 +84,9 @@ jobs:
         name: python-package-distributions
         path: dist/
 
+    - name: Install twine
+      run: pip install twine
+    
     - name: Publish to PyPI
       env:
         TWINE_USERNAME: __token__