[ci] Run Windows Arm64 build tests post-submit (#6166)

The Flutter try pool does not have any Windows Arm64 machines. Thus, any Windows Arm64 pre-submit tests would fail without `bringup: true` as there's no machines to run them.

This change will allow us to promote the Windows Arm64 build tests out of `bringup`.

See: flutter/flutter#141986
Part of flutter/flutter#129813

Author: loic-sharma

.ci.yaml

@@ -1472,6 +1472,7 @@ targets:
 
   - name: Windows_arm64 windows-build_all_packages master
     recipe: packages/packages
+    presubmit: false
     timeout: 30
     bringup: true # https://github.com/flutter/flutter/issues/134083
     properties:
@@ -1506,6 +1507,7 @@ targets:
 
   - name: Windows_arm64 windows-build_all_packages stable
     recipe: packages/packages
+    presubmit: false
     timeout: 30
     bringup: true
     properties: