Migrate a miscellaneous set of libraries to Gradle version catalogs

Test: ./gradlew tasks
Change-Id: I47c569e94bb1caa50a42b8eb60274e027b769226
diff --git a/placeholder-tests/build.gradle b/placeholder-tests/build.gradle
index 863ce958..f96a629c6 100644
--- a/placeholder-tests/build.gradle
+++ b/placeholder-tests/build.gradle
@@ -14,19 +14,17 @@
  * limitations under the License.
  */
 
-import static androidx.build.dependencies.DependenciesKt.*
-
 plugins {
     id("AndroidXPlugin")
     id("com.android.library")
 }
 
 dependencies {
-    testImplementation(JUNIT)
-    androidTestImplementation(ANDROIDX_TEST_EXT_JUNIT)
-    androidTestImplementation(ANDROIDX_TEST_CORE)
-    androidTestImplementation(ANDROIDX_TEST_RUNNER)
-    androidTestImplementation(ANDROIDX_TEST_RULES)
+    testImplementation(libs.junit)
+    androidTestImplementation(libs.testExtJunit)
+    androidTestImplementation(libs.testCore)
+    androidTestImplementation(libs.testRunner)
+    androidTestImplementation(libs.testRules)
 }
 
 androidx {