[EN-3260] Added 3.9 to testpackage workflow

Author: asalynskii

.github/workflows/testpackage.yml

@@ -48,7 +48,7 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-18.04, windows-latest, macos-latest]
-        python-version: [3.6, 3.7, 3.8]
+        python-version: [3.6, 3.7, 3.8, 3.9]
 
     runs-on: ${{ matrix.os }}