Upgrade cpython3 to the latest 3.8.9 build.

Bug: 1184767
Change-Id: I62794e383bad8592ae1027b728426042a843c610
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2846742
Commit-Queue: Brian Ryner <bryner@google.com>
Reviewed-by: Robbie Iannucci <iannucci@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@google.com>

bootstrap/manifest.txt

@@ -23,7 +23,7 @@ infra/3pp/tools/cpython/${os}-${arch=amd64} version:2.7.17.chromium.22
 
 # TODO(https://crbug.com/1103326): Remove `=amd64` once mac/arm64 python3 exists
 @Subdir python3
-infra/3pp/tools/cpython3/${os}-${arch=amd64} version:3.8.0.chromium.8
+infra/3pp/tools/cpython3/${os}-${arch=amd64} version:2@3.8.9.chromium.14
 
 # TODO(https://crbug.com/1184766): Remove `=amd64` once mac/arm64 git exists
 @Subdir git