Run worklflows on 3.9 instead of 3.7

Change-Id: Ief9ad55fcc695ad5480f6568b9a71e3d70f56beb
diff --git a/.github/workflows/pythonpackage.yml b/.github/workflows/pythonpackage.yml
index b534161..767a5c1 100644
--- a/.github/workflows/pythonpackage.yml
+++ b/.github/workflows/pythonpackage.yml
@@ -10,16 +10,16 @@
       max-parallel: 4
       fail-fast: false
       matrix:
-        python-version: [3.7, 3.8]
+        python-version: [3.9, 3.8]
         r-version: [3.6, release]
         os: [windows-latest, macOS-latest]
         exclude:
           - os: macOS-latest
-            python-version: 3.7
+            python-version: 3.9
           - os: macOS-latest
             r-version: 3.6
           - os: windows-latest
-            python-version: 3.7
+            python-version: 3.9
           - os: windows-latest
             r-version: 3.6
           - os: ubuntu-latest