Update cpython3 package to the latest 3.8 build for bleeding-edge.

This is a prerequisite to enabling the native Mac ARM64 cpython3,
since we don't have that package built at the old 3.8.0 version.

Bug: 1184767
Change-Id: I68a7de836f9fae25ecbb2fc84aff389a24c32e5d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2842053Reviewed-by: Dirk Pranke <dpranke@google.com>
Commit-Queue: Brian Ryner <bryner@google.com>

bootstrap/manifest_bleeding_edge.txt

@@ -21,7 +21,7 @@ $VerifiedPlatform windows-386 windows-amd64 linux-amd64 mac-amd64
 infra/3pp/tools/cpython/${platform} version:2.7.17.chromium.22
 
 @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.13
 
 @Subdir git
 infra/3pp/tools/git/${os}-${arch} version:2@2.30.2.chromium.6