Make ProgramInformation final.

This was likely an oversight when first importing #4930.

PiperOrigin-RevId: 369199775

library/dash/src/main/java/com/google/android/exoplayer2/source/dash/manifest/ProgramInformation.java

@@ -19,7 +19,7 @@ import androidx.annotation.Nullable;
 import com.google.android.exoplayer2.util.Util;
 
 /** A parsed program information element. */
-public class ProgramInformation {
+public final class ProgramInformation {
   /** The title for the media presentation. */
   @Nullable public final String title;