upgrade git to 2.26.1

Bug: 1070694
Change-Id: I47def761c61ea62f44aa891f869383b9a0a56d2b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2149755Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>
Commit-Queue: Anthony Polito <apolito@google.com>

bootstrap/manifest.txt

@@ -24,4 +24,4 @@ infra/3pp/tools/cpython/${platform} version:2.7.17.chromium.22
 infra/3pp/tools/cpython3/${os}-${arch} version:3.8.0.chromium.8
 
 @Subdir git
-infra/3pp/tools/git/${os}-${arch} version:2.24.1.chromium.5
+infra/3pp/tools/git/${os}-${arch} version:2.26.1.chromium.6

bootstrap/manifest_bleeding_edge.txt

@@ -24,4 +24,4 @@ infra/3pp/tools/cpython/${platform} version:2.7.17.chromium.22
 infra/3pp/tools/cpython3/${os}-${arch=amd64} version:3.8.0.chromium.8
 
 @Subdir git
-infra/3pp/tools/git/${os}-${arch} version:2.24.1.chromium.5
+infra/3pp/tools/git/${os}-${arch} version:2.26.1.chromium.6