Fix half sheet class name not match issue.

Test: half sheet shows up
Bug: 218232824
Change-Id: I392e0db51bd3725985af8b7b769c3f3b55e4a42c
diff --git a/nearby/halfsheet/AndroidManifest.xml b/nearby/halfsheet/AndroidManifest.xml
index 3df7970..22987fb 100644
--- a/nearby/halfsheet/AndroidManifest.xml
+++ b/nearby/halfsheet/AndroidManifest.xml
@@ -20,6 +20,7 @@
         <activity
             android:name="com.android.nearby.halfsheet.HalfSheetActivity"
             android:exported="true"
+            android:launchMode="singleInstance"
             android:theme="@style/HalfSheetStyle" >
             <intent-filter>
                 <action android:name="android.nearby.SHOW_HALFSHEET"/>