Fix header name in WebServerDispatcher used for testing

HTTP header names are case-insensitive, but all the others in this file
are 'correctly' cased, so we might as well be consistent.

PiperOrigin-RevId: 408840566

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

@@ -261,7 +261,7 @@ public class WebServerDispatcher extends Dispatcher {
     Resource resource = checkNotNull(resourcesByPath.get(requestPath));
     byte[] resourceData = resource.getData();
     if (resource.supportsRangeRequests()) {
-      response.setHeader("Accept-ranges", "bytes");
+      response.setHeader("Accept-Ranges", "bytes");
     }
     @Nullable ImmutableMap<String, Float> acceptEncodingHeader = getAcceptEncodingHeader(request);
     @Nullable String preferredContentCoding;