Add Python3.8 to Kokoro windows

tools/internal_ci/helper_scripts/prepare_build_windows.bat

@@ -35,6 +35,14 @@ python -m pip install google-api-python-client
 powershell -File src\csharp\install_dotnet_sdk.ps1
 set PATH=%LOCALAPPDATA%\Microsoft\dotnet;%PATH%
 
+@rem Install Python 3.8.0
+powershell -command "(New-Object Net.WebClient).DownloadFile('https://www.python.org/ftp/python/3.8.0/python-3.8.0-amd64.exe', 'C:\tools\python-3.8.0-amd64.exe')"
+powershell -command "& 'C:\tools\python-3.8.0-amd64.exe' /quiet InstallAllUsers=1 PrependPath=1 Include_test=0 TargetDir='C:\Python38'"
+
+@rem Install Python 3.8.0 32 Bit Version
+powershell -command "(New-Object Net.WebClient).DownloadFile('https://www.python.org/ftp/python/3.8.0/python-3.8.0.exe', 'C:\tools\python-3.8.0.exe')"
+powershell -command "& 'C:\tools\python-3.8.0.exe' /quiet InstallAllUsers=1 PrependPath=1 Include_test=0 TargetDir='C:\Python38_32bit'"
+
 @rem Newest version of Go is required to be able to build boringssl with cmake
 @rem TODO(jtattermusch): try to eliminate the dependency on Go
 choco install golang -y --version 1.13.1 --limit-output

tools/run_tests/artifacts/artifact_targets.py

@@ -412,14 +412,12 @@ def targets():
         PythonArtifact('windows', 'x86', 'Python35_32bits'),
         PythonArtifact('windows', 'x86', 'Python36_32bits'),
         PythonArtifact('windows', 'x86', 'Python37_32bits'),
-        # TODO(https://github.com/grpc/grpc/issues/20615) Enable this artifact
-        # PythonArtifact('windows', 'x86', 'Python38_32bits'),
+        PythonArtifact('windows', 'x86', 'Python38_32bits'),
         PythonArtifact('windows', 'x64', 'Python27'),
         PythonArtifact('windows', 'x64', 'Python35'),
         PythonArtifact('windows', 'x64', 'Python36'),
         PythonArtifact('windows', 'x64', 'Python37'),
-        # TODO(https://github.com/grpc/grpc/issues/20615) Enable this artifact
-        # PythonArtifact('windows', 'x64', 'Python38'),
+        PythonArtifact('windows', 'x64', 'Python38'),
         RubyArtifact('linux', 'x64'),
         RubyArtifact('macos', 'x64'),
         PHPArtifact('linux', 'x64')