Fix tapas for git_main builds

In the git_main trunk stable builds, we're required to have a
TARGET_RELEASE set.

For now, we hard-code this to "trunk_staging" (and leave a TODO
to accept this as a function argument).

This will have us producing valid builds under git_main.

Bug: 307975293
Test: 'tapas google-tradefed-all' now works on a tree that has go/aog/2806253
Change-Id: I70572fb4c7902350513e251694f3ddef91efcb13
diff --git a/envsetup.sh b/envsetup.sh
index 2ea5507..f4cba1d 100644
--- a/envsetup.sh
+++ b/envsetup.sh
@@ -887,6 +887,8 @@
 {
     local showHelp="$(echo $* | xargs -n 1 echo | \grep -E '^(help)$' | xargs)"
     local arch="$(echo $* | xargs -n 1 echo | \grep -E '^(arm|x86|arm64|x86_64)$' | xargs)"
+    # TODO(b/307975293): Expand tapas to take release arguments (and update hmm() usage).
+    local release="trunk_staging"
     local variant="$(echo $* | xargs -n 1 echo | \grep -E '^(user|userdebug|eng)$' | xargs)"
     local density="$(echo $* | xargs -n 1 echo | \grep -E '^(ldpi|mdpi|tvdpi|hdpi|xhdpi|xxhdpi|xxxhdpi|alldpi)$' | xargs)"
     local keys="$(echo $* | xargs -n 1 echo | \grep -E '^(devkeys)$' | xargs)"
@@ -902,6 +904,10 @@
         echo "tapas: Error: Multiple build archs supplied: $arch"
         return
     fi
+    if [ $(echo $release | wc -w) -gt 1 ]; then
+        echo "tapas: Error: Multiple build releases supplied: $release"
+        return
+    fi
     if [ $(echo $variant | wc -w) -gt 1 ]; then
         echo "tapas: Error: Multiple build variants supplied: $variant"
         return
@@ -936,6 +942,7 @@
     fi
 
     export TARGET_PRODUCT=$product
+    export TARGET_RELEASE=$release
     export TARGET_BUILD_VARIANT=$variant
     export TARGET_BUILD_DENSITY=$density
     export TARGET_BUILD_TYPE=release