Close ServerContext before Executor in AbstractNettyHttpServerTest (#…

…1101)

Motivation:

Because the server's executor is closed before the server, all tests
from `AbstractNettyHttpServerTest` subclasses print
`TaskBasedSignalOffloader - Failed to execute task on the executor`
errors that pollute logs and make the build log unreadable.

Modifications:

- Close `ServerContext` before `Executor` in `AbstractNettyHttpServerTest`;

Result:

No `TaskBasedSignalOffloader` errors in test logs.

servicetalk-http-netty/src/test/java/io/servicetalk/http/netty/AbstractNettyHttpServerTest.java

@@ -180,7 +180,7 @@ protected void service(final StreamingHttpService service) {
 
     @After
     public void stopServer() throws Exception {
-        newCompositeCloseable().appendAll(httpConnection, httpClient, clientExecutor, serverExecutor, serverContext)
+        newCompositeCloseable().appendAll(httpConnection, httpClient, clientExecutor, serverContext, serverExecutor)
                 .close();
     }