cos-gpu-installer-v1: forcefully umount /usr/bin

BUG=b/264620262

Change-Id: If1225ad976362e65ed9728abb35cb49094099196
Reviewed-on: https://cos-review.googlesource.com/c/cos/tools/+/40940
Tested-by: Arnav Kansal <rnv@google.com>
Cloud-Build: GCB Service account <228075978874@cloudbuild.gserviceaccount.com>
Reviewed-by: Meena Shanmugam <meenashanmugam@google.com>
diff --git a/src/cmd/cos_gpu_installer_v1/cos-gpu-installer-docker/entrypoint.sh b/src/cmd/cos_gpu_installer_v1/cos-gpu-installer-docker/entrypoint.sh
index abde8f5..54d574c 100755
--- a/src/cmd/cos_gpu_installer_v1/cos-gpu-installer-docker/entrypoint.sh
+++ b/src/cmd/cos_gpu_installer_v1/cos-gpu-installer-docker/entrypoint.sh
@@ -414,7 +414,7 @@
   update_container_ld_cache
 
   # Install an exit handler to cleanup the overlayfs mount points.
-  trap "{ umount /lib/modules/\"$(uname -r)\"/video; umount -fl /usr/lib/x86_64-linux-gnu ; umount /usr/bin; }" EXIT
+  trap "{ umount /lib/modules/\"$(uname -r)\"/video; umount -fl /usr/lib/x86_64-linux-gnu ; umount -fl /usr/bin; }" EXIT
   popd
 }