Make package.yml workflow test code on Python 3.9

Author: althonos

.github/workflows/package.yml

@@ -60,6 +60,10 @@ jobs:
       uses: actions/checkout@v2
       with:
         submodules: true
+    - name: Setup Python 3.9
+      uses: actions/setup-python@v2
+      with:
+        python-version: 3.9
     - name: Download source distribution
       uses: actions/download-artifact@v2
       with:
@@ -84,7 +88,11 @@ jobs:
       uses: actions/checkout@v2
       with:
         submodules: true
-    - name: Download source distribution
+    - name: Setup Python 3.9
+      uses: actions/setup-python@v2
+      with:
+        python-version: 3.9
+    - name: Download wheel distribution
       uses: actions/download-artifact@v2
       with:
           name: dist

tests/mark.py

@@ -1,2 +1,2 @@
-def slow(self):
-    pass
+def slow(cls):
+    return cls