Update stable image to R28-4100.7.0.

Update the stable image for repair. There have been some new board
additions that are no longer covered by the previous R25 release.

This image is a shipped image on daisy_spring and suite runs in the
autotest results db look green for other platforms.

TEST=repaired daisy_spring host
BUG=chromium:242184

Change-Id: I11138ab79b883fd295e1b93ebe362a109b9f9044
Reviewed-on: https://gerrit.chromium.org/gerrit/55759
Tested-by: Scott Zawalski <scottz@chromium.org>
Reviewed-by: Dan Shi <dshi@chromium.org>
Reviewed-by: Fang Deng <fdeng@chromium.org>
Commit-Queue: Scott Zawalski <scottz@chromium.org>
Reviewed-by: Scott Zawalski <scottz@chromium.org>
diff --git a/global_config.ini b/global_config.ini
index ae430a3..5753d72 100644
--- a/global_config.ini
+++ b/global_config.ini
@@ -139,7 +139,7 @@
 serve_packages_from_autoserv: True
 
 [CROS]
-stable_cros_version: R25-3428.149.0
+stable_cros_version: R28-4100.7.0
 stable_build_pattern: %s-release/%s
 # The zone that all Chrome OS devices are in if they are in a lab.
 dns_zone: cros.corp.google.com