Have default 'lunch' target use a release type

In git_main, the correct target here is aosp_arm-trunk_staging-eng
(or "trunk_food" or "next", but we choose the most generic
"trunk_staging").

Bug: 307738446
Test: "lunch", hit return for the default, "echo $TARGET_RELEASE" to confirm
Change-Id: I4d4bcaf27553976e64133c7351db296953f88b08
diff --git a/envsetup.sh b/envsetup.sh
index e448bd3..2ea5507 100644
--- a/envsetup.sh
+++ b/envsetup.sh
@@ -774,7 +774,7 @@
         answer=$1
     else
         print_lunch_menu
-        echo "Which would you like? [aosp_arm-eng]"
+        echo "Which would you like? [aosp_arm-trunk_staging-eng]"
         echo -n "Pick from common choices above (e.g. 13) or specify your own (e.g. aosp_barbet-eng): "
         read answer
         used_lunch_menu=1
@@ -784,7 +784,7 @@
 
     if [ -z "$answer" ]
     then
-        selection=aosp_arm-eng
+        selection=aosp_arm-trunk_staging-eng
     elif (echo -n $answer | grep -q -e "^[0-9][0-9]*$")
     then
         local choices=($(TARGET_BUILD_APPS= get_build_var COMMON_LUNCH_CHOICES))