Tweak lunch choice for git_main

We add "trunk_staging-" in our COMMON_LUNCH_CHOICES so it will
be a valid target in the way trunk stable lunch targets are
parsed.

Bug: 307738446
Test: None
Change-Id: I005b8d16c5bab23f7e456ec71a2e062bfd5199c7
diff --git a/populate-new-device.sh b/populate-new-device.sh
index db5da3d..013e8fe 100755
--- a/populate-new-device.sh
+++ b/populate-new-device.sh
@@ -43,7 +43,7 @@
 
 PRODUCT_MAKEFILES := \$(LOCAL_DIR)/full_$2.mk
 
-COMMON_LUNCH_CHOICES := full_$2-userdebug
+COMMON_LUNCH_CHOICES := full_$2-trunk_staging-userdebug
 EOF
 
 cat > device/$1/$2/full_$2.mk << EOF