Update Python version in CI

Author: valeros

.github/workflows/tests.yml

@@ -8,7 +8,7 @@ jobs:
       fail-fast: false
       matrix:
         os: [ubuntu-latest, windows-latest, macos-latest]
-        python-version: [3.7]
+        python-version: [3.9]
         example:
           - "examples/espidf-hello-world"
     runs-on: ${{ matrix.os }}