Settings: Annotate JUnit4 test with @Test

Mollify Errorprone.

Bug: 72076216
Bug: 73796195
Test: m javac-check RUN_ERROR_PRONE=true
Test: m RunSettingsRoboTests
Test: atest WifiSettingsUiTest
Change-Id: I9bc950f0ecf8d6de89b9401ea4cf1c50fd3acbcd

tests/robotests/src/com/android/settings/MasterClearTest.java

@@ -355,6 +355,7 @@ public class MasterClearTest {
         assertEquals(TEST_CONFIRMATION_CLASS, actualIntent.getComponent().getClassName());
     }
 
+    @Test
     public void testShowAccountCredentialConfirmation() {
         // Finally mock out the startActivityForResultCall
         doNothing().when(mMasterClear)