Merge "Update go.mod to 1.21" into main am: 9e4744383a

Original change: https://android-review.googlesource.com/c/platform/build/+/2874720

Change-Id: Ibf09b603acc3330155dd8cd90f502845a524357d
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>