Fix lunch choices for git_main

We add "trunk_staging-" for all COMMON_LUNCH_CHOICES so they are
valid in the trunk stable setup.

Bug: 307738446
Test: lunch
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:ae5df6c5a3228f450189be167ef1203477db950b)
Merged-In: I7b31c905be1d994de52652162c0bd2bc8c5b8c65
Change-Id: I7b31c905be1d994de52652162c0bd2bc8c5b8c65

AndroidProducts.mk

@@ -20,4 +20,4 @@ PRODUCT_MAKEFILES := \
     $(LOCAL_DIR)/factory_lynx.mk
 
 COMMON_LUNCH_CHOICES := \
-    aosp_lynx-userdebug
+    aosp_lynx-trunk_staging-userdebug