fix: Android release builds broken due to missing color (#5909)

d9fde31 introduced
  Release build errors by introducing a reference to
  the color 'background_black', which is set in experimental
  builds but not release builds.

Signed-off-by: David Li <jiawei.davidli@gmail.com>

android/app/src/main/res/values/colors.xml

@@ -1,6 +1,7 @@
 <?xml version="1.0" encoding="utf-8"?>
 <resources>
     <color name="black">#000000</color>
+    <color name="background_black">#090A11</color>
     <color name="accent_material_dark">#009926</color>
     <color name="primary_material_dark">#212121</color>
     <color name="background_material_dark">#212121</color>