Roll new cpython(3) packages to depot_tools.

This contains
https://chromium-review.googlesource.com/c/infra/infra/+/2943752 , a
stability fix for Mac (and potential startup performance improvement).

Bug: 1215121
Change-Id: I77a90b8b00ddf0570dc8e0e5821c0b31b60ab79a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2951423
Reviewed-by: Dirk Pranke <dpranke@google.com>
Commit-Queue: Brian Ryner <bryner@google.com>

bootstrap/manifest.txt

@@ -18,10 +18,10 @@
 $VerifiedPlatform windows-amd64 linux-amd64 mac-amd64
 
 @Subdir python
-infra/3pp/tools/cpython/${platform} version:2@2.7.18.chromium.36
+infra/3pp/tools/cpython/${platform} version:2@2.7.18.chromium.39
 
 @Subdir python3
-infra/3pp/tools/cpython3/${platform} version:2@3.8.10.chromium.17
+infra/3pp/tools/cpython3/${platform} version:2@3.8.10.chromium.19
 
 # TODO(https://crbug.com/1184766): Remove `=amd64` once mac/arm64 git exists
 @Subdir git