Mark mendel-day repos as trusted

E: The repository 'http://packages.cloud.google.com/apt mendel-day InRelease' is not signed.
E: The repository 'http://packages.cloud.google.com/apt mendel-bsp-enterprise-day InRelease' is not signed.

Change-Id: I2b66b6fa59d9cf0e87b2bd3a506b59234bda971c
diff --git a/packages.mk b/packages.mk
index af655b0..aa16b9b 100644
--- a/packages.mk
+++ b/packages.mk
@@ -28,7 +28,7 @@
 	mkdir -p $(ROOTDIR)/cache
 	sudo pbuilder create \
 		--basetgz $@ \
-		--othermirror "deb http://packages.cloud.google.com/apt mendel-day main|deb http://packages.cloud.google.com/apt mendel-bsp-$(BOARD_NAME)-day main" \
+		--othermirror "deb [trusted=yes] http://packages.cloud.google.com/apt mendel-day main|deb [trusted=yes] http://packages.cloud.google.com/apt mendel-bsp-$(BOARD_NAME)-day main" \
 		--distribution buster \
 		--architecture amd64 \
 		--extrapackages "crossbuild-essential-armhf crossbuild-essential-arm64 debhelper gnupg lintian"