Bug 40064: Use Gecko Beta for Nightly and Debug variants

app/build.gradle

@@ -327,9 +327,9 @@ ext.gleanDocsDirectory = "$rootDir/docs"
 apply plugin: "org.mozilla.telemetry.glean-gradle-plugin"
 
 dependencies {
-    debugImplementation Deps.mozilla_browser_engine_gecko_nightly
+    debugImplementation Deps.mozilla_browser_engine_gecko_beta
 
-    nightlyImplementation Deps.mozilla_browser_engine_gecko_nightly
+    nightlyImplementation Deps.mozilla_browser_engine_gecko_beta
     betaImplementation Deps.mozilla_browser_engine_gecko_beta
     releaseImplementation Deps.mozilla_browser_engine_gecko_release