RequestManageCredentials dark theme

Manual testing steps
* Enable dark theme via Settings > display
* Install TestDPC and select 'Request to manage credentials'
* Verify dark theme is displayed (including light text)

Bug: 177901172
Test: atest com.android.settings.security.RequestManageCredentialsTest
      manual testing
Change-Id: I6db1361ffcbf1e193673eb5ca7ef3f403d5023b1
diff --git a/AndroidManifest.xml b/AndroidManifest.xml
index ce80fc5..fa2bbc9 100644
--- a/AndroidManifest.xml
+++ b/AndroidManifest.xml
@@ -1459,7 +1459,7 @@
         </activity>
 
         <activity android:name=".security.RequestManageCredentials"
-                  android:theme="@style/Theme.RequestManageCredentials"
+                  android:theme="@style/Theme.SubSettings"
                   android:exported="true">
             <intent-filter>
                 <action android:name="android.security.MANAGE_CREDENTIALS"/>