explicitly use python3 in workflow for clarity's sake

Author: qrkourier

.github/workflows/main.yml

@@ -21,7 +21,7 @@ jobs:
     steps:
     - uses: actions/checkout@v2
       with:
-        fetch-depth: 0 # unshallow checkout enables setuptools_scm to infer PyPi version from Git tags
+        fetch-depth: 0 # unshallow checkout enables setuptools_scm to infer PyPi version from Git
 
     - name: Set up Python
       uses: actions/setup-python@v2
@@ -30,11 +30,11 @@ jobs:
 
     - name: Install dependencies
       run: |
-        python -m pip install --upgrade pip
-        pip install build
+        python3 -m pip install --upgrade pip
+        pip3 install build
 
     - name: Build Package
-      run: python -m build
+      run: python3 -m build
 
     - name: Publish Test Package
       uses: pypa/gh-action-pypi-publish@27b31702a0e7fc50959f5ad993c78deac1bdfc29