Reduce flakiness in TomcatServlet5Test.requestWithException() (#18486)

Author: trask

instrumentation/servlet/servlet-5.0/testing/src/main/java/io/opentelemetry/javaagent/instrumentation/servlet/v5_0/TestServlet5.java

@@ -236,7 +236,14 @@ protected void service(HttpServletRequest req, HttpServletResponse resp) throws
                 resp.sendError(endpoint.getStatus(), endpoint.getBody());
               } else if (EXCEPTION.equals(endpoint)) {
                 resp.setStatus(endpoint.getStatus());
-                resp.getWriter().print(endpoint.getBody());
+                PrintWriter writer = resp.getWriter();
+                writer.print(endpoint.getBody());
+                if (req.getClass().getName().contains("catalina")) {
+                  // on tomcat close the writer to ensure response is sent immediately,
+                  // otherwise there is a chance that tomcat resets the connection before the
+                  // response is sent
+                  writer.close();
+                }
                 throw new IllegalStateException(endpoint.getBody());
               } else if (HTML_PRINT_WRITER.equals(endpoint)) {
                 // intentionally testing setting status before contentType here to cover that case