git: upgraded package to upstream

Upgraded dev-vcs/git to version 2.26.3 on amd64

BUG=b/183757778
TEST=presubmit
RELEASE_NOTE=Upgraded dev-vcs/git to version 2.26.3. Resolves CVE-2021-21300

cos-patch: lts-refresh
Change-Id: I2ffa00fa1a8eeafe34b259aea6790599c33743aa
Reviewed-on: https://cos-review.googlesource.com/c/third_party/overlays/portage-stable/+/15851
Tested-by: Cusky Presubmit Bot <presubmit@cos-infra-prod.iam.gserviceaccount.com>
Main-Branch-Verified: Cusky Presubmit Bot <presubmit@cos-infra-prod.iam.gserviceaccount.com>
Reviewed-by: Robert Kolchmeyer <rkolchmeyer@google.com>
7 files changed