Move DSL namespace from supportLibrary to androidx.

Test: ./gradlew createArchive
Change-Id: I07a66c4685daec2b72c83a8fbff9430ec9764a64
diff --git a/navigation/testing/build.gradle b/navigation/testing/build.gradle
index 0076dcf..de207d42 100644
--- a/navigation/testing/build.gradle
+++ b/navigation/testing/build.gradle
@@ -50,7 +50,7 @@
     androidTestImplementation(ESPRESSO_CORE)
 }
 
-supportLibrary {
+androidx {
     name = "Android Navigation Testing"
     publish = false
     mavenVersion = LibraryVersions.NAVIGATION_TESTING