Fix resource problem in SettingsSliderPreferenceControllerTest

Somehow Resource IDs are inconsistent between Settings and
SettingsUnitTests. Import SettingsLibTwoTargetPreference to fix.

Bug: 183340630
Test: atest SettingsSliderPreferenceControllerTest
Change-Id: Icc404d8ebefe1399806775272a37c56845406bc7
diff --git a/tests/unit/Android.bp b/tests/unit/Android.bp
index b7ac4b1..408f2d3 100644
--- a/tests/unit/Android.bp
+++ b/tests/unit/Android.bp
@@ -34,6 +34,7 @@
         "ub-uiautomator",
         "SettingsLibSettingsSpinner",
         "SettingsLibUsageProgressBarPreference",
+        "SettingsLibTwoTargetPreference",
     ],
 
     // Include all test java files.