[DDM] enable host builds in the merge queue (#177446)

Follow-up to https://github.com/flutter/flutter/pull/177252.
Towards b/452833651.
Similar to https://github.com/flutter/flutter/pull/168233.

This changes the ddm host build to be part of the merge queue so they
are available on every commit because we want to use them for internal
testing and use them on CI internally.

engine/src/flutter/.ci.yaml

diff --git a/engine/src/flutter/.ci.yaml b/engine/src/flutter/.ci.yaml
index f326891..284512e 100644
--- a/engine/src/flutter/.ci.yaml
+++ b/engine/src/flutter/.ci.yaml
@@ -233,13 +233,12 @@
 
   - name: Linux linux_host_engine_ddm
     recipe: engine_v2/engine_v2
-    bringup: true
-    backfill: false
     timeout: 120
     enabled_branches:
       # Don't run this on release branches
       - master
     properties:
+      release_build: "true"
       add_recipes_cq: "true"
       config_name: linux_host_engine_ddm
     # Do not remove(https://github.com/flutter/flutter/issues/144644)