Bug 1897176 - Allow unit tests to access and use app resources. r=tthibaud

Differential Revision: https://phabricator.services.mozilla.com/D223722

build.gradle

@@ -139,6 +139,9 @@ allprojects {
         if (it.hasProperty('android')) {
             android {
                 buildToolsVersion gradle.mozconfig.substs.ANDROID_BUILD_TOOLS_VERSION
+                testOptions {
+                    unitTests.includeAndroidResources = true
+                }
             }
         }
     }