Throw RuntimeException instead of Error from ExoHostedTest

Throwing Error forces a test to catch Throwable (e.g.
DashWidevineOfflineTest#widevineOfflineReleasedV22), which will also
catch AssertionError meaning the fail() call at the end of the try block
won't work.

The DashWidevineOfflineTest have been broken since
https://github.com/google/ExoPlayer/commit/91185500a1242b99b86b18bc9f3449d3dac1fa01

PiperOrigin-RevId: 331120894

testutils/src/main/java/com/google/android/exoplayer2/testutil/ExoHostedTest.java

@@ -157,7 +157,7 @@ public abstract class ExoHostedTest implements AnalyticsListener, HostedTest {
   @Override
   public final void onFinished() {
     if (failOnPlayerError && playerError != null) {
-      throw new Error(playerError);
+      throw new RuntimeException(playerError);
     }
     logMetrics(audioDecoderCounters, videoDecoderCounters);
     if (expectedPlayingTimeMs != EXPECTED_PLAYING_TIME_UNSET) {