CI: update the zephyr submodule to grab HEAD

Always using HEAD will help us detect errors faster instead of when we
manually update to a new SHA.

Change-Id: I1730a7a6f62939d1f9023827755466142efcb4a6
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/zephyr-integration/+/100441
Commit-Queue: Yuval Peress <peress@google.com>
Reviewed-by: Rob Mohr <mohrr@google.com>
diff --git a/.gitmodules b/.gitmodules
index 47c5be8..8dd1dfc 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -4,3 +4,4 @@
 [submodule "zephyr"]
 	path = zephyr
 	url = ../../third_party/github/zephyrproject-rtos/zephyr
+	branch = main
diff --git a/zephyr b/zephyr
index 7f6b762..a1ef368 160000
--- a/zephyr
+++ b/zephyr
@@ -1 +1 @@
-Subproject commit 7f6b762a734b793a031103e12bbce865645d4f90
+Subproject commit a1ef368094f754643fa07d55411c77a53c3a6297