Add missed "optional_uses_libs" to avoid testing failed

After adding the missed "optional_uses_libs" I can run the SettingsRoboTests test locally (screenshot: https://screenshot.googleplex.com/3nLrCwX4bLHGxvP)

Bug: 203408618
Test: make SettingsRoboTests
Change-Id: I1bfdb2204fe89c8d0dbcfb347d10fa74853051e9
diff --git a/tests/robotests/Android.bp b/tests/robotests/Android.bp
index 43bcec7..bc25377 100644
--- a/tests/robotests/Android.bp
+++ b/tests/robotests/Android.bp
@@ -60,6 +60,10 @@
         "ims-common",
     ],
     uses_libs: ["org.apache.http.legacy"],
+    optional_uses_libs: [
+        "androidx.window.extensions",
+        "androidx.window.sidecar",
+    ],
 }
 
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