ci: add python 3.9 test runners

.codecov.yml

@@ -3,7 +3,7 @@ codecov:
     require_ci_to_pass: true
     # wait until at all test runners have uploaded a report (see the test job's build matrix)
     # otherwise, coverage failures may be shown while some reports are still missing
-    after_n_builds: 10
+    after_n_builds: 12
 comment:
   # this also configures the layout of PR check summaries / comments
   layout: "reach, diff, flags, files"

.github/workflows/main.yml

@@ -21,7 +21,7 @@ jobs:
       # when changing the build matrix and changing the number of test runners
       matrix:
         os: [ubuntu-latest, windows-latest]
-        python: [2.7, 3.5, 3.6, 3.7, 3.8]
+        python: [2.7, 3.5, 3.6, 3.7, 3.8, 3.9]
 #       include:
 #         - python: X.Y-dev
 #           continue: true
@@ -29,7 +29,7 @@ jobs:
     timeout-minutes: 60
     steps:
       - uses: actions/checkout@v2
-      - uses: actions/setup-python@v1
+      - uses: actions/setup-python@v2
         with:
           python-version: ${{ matrix.python }}
       - name: Install dependencies