Update CI to Python 3.9 (#1443)

Since the pulumi/pulumi#17883 change Pulumi no
longer supports 3.8 and tests need to be performed on 3.9 or later
versions of Python.

Author: t0yv0

.github/actions/install/action.yml

@@ -24,9 +24,9 @@ runs:
         registry-url: https://registry.npmjs.org
 
     - name: Setup Python
-      uses: actions/setup-python@v4
+      uses: actions/setup-python@v5
       with:
-        python-version: "3.8"
+        python-version: "3.9"
 
     - name: Setup DotNet
       if: inputs.skip_dotnet_and_java != 'true'