Update publish.yml

Pin Python version to fix publishing error

Author: mikeheddes

.github/workflows/publish.yml

@@ -15,7 +15,7 @@ jobs:
     - name: Set up Python
       uses: actions/setup-python@v3
       with:
-        python-version: 3.x
+        python-version: 3.12
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip
@@ -36,7 +36,7 @@ jobs:
     - name: Set up Python
       uses: actions/setup-python@v3
       with:
-        python-version: 3.x
+        python-version: 3.12
     - name: Add conda to system path
       run: |
         # $CONDA is an environment variable pointing to the root of the miniconda directory