sys-boot/shim: update to 15.5

Update RH EFI shim to version 15.5.

BUG=b/229406221
TEST=presubmit
RELEASE_NOTE=Upgraded package sys-boot/shim to version 15.5.

Change-Id: I5330cf81f9e88b685dfe5065edaf79383944416e
Reviewed-on: https://cos-review.googlesource.com/c/cos/overlays/board-overlays/+/32283
Reviewed-by: Meena Shanmugam <meenashanmugam@google.com>
Reviewed-by: Roy Yang <royyang@google.com>
Tested-by: Cusky Presubmit Bot <presubmit@cos-infra-prod.iam.gserviceaccount.com>
5 files changed