CI: Skip python setup when already installed

Author: ByteOtter

.github/workflows/pytests.yml

@@ -30,7 +30,17 @@ jobs:
             echo "cache_type=pip" >> $GITHUB_OUTPUT
           fi
 
+      - name: Check for Python
+        id: python-check
+        run: |
+          if command -v python &/dev/null; then
+            echo "python_installed=true" >> $GITHUB_OUTPUT
+          else
+            echo "python_installed=false" >> $GITHUB_OUTPUT
+          fi
+
       - name: Set up Python
+        if: steps.python-check.outputs.python_installed == 'false'
         uses: actions/setup-python@v5
         with:
           python-version: '3.13'