End grpc server span in onComplete instead of close

[laurit]

Resolves #10988

javadoc of close follows

  /**
   * Close the call with the provided status. No further sending or receiving will occur. If {@link
   * Status#isOk} is {@code false}, then the call is said to have failed.
   *
   * <p>If no errors or cancellations are known to have occurred, then a {@link Listener#onComplete}
   * notification should be expected, independent of {@code status}. Otherwise {@link
   * Listener#onCancel} has been or will be called.
   *
   * <p>Since {@link Metadata} is not thread-safe, the caller must not access (read or write) {@code
   * trailers} after this point.
   *
   * <p>This method implies the caller completed processing the RPC, but it does not imply the RPC
   * is complete. The call implementation will need additional time to complete the RPC and during
   * this time the client is still able to cancel the request or a network error might cause the
   * RPC to fail. If you wish to know when the call is actually completed/closed, you have to use
   * {@link Listener#onComplete} or {@link Listener#onCancel} instead. This method is not
   * necessarily invoked when Listener.onCancel() is called.
   *
   * @throws IllegalStateException if call is already {@code close}d
   */
  public abstract void close(Status status, Metadata trailers);

[zeitlinger]

why is there no change in a test?