Fix async blocking flag set before commit confirmation

NettyBlockResponseFunction.tryCommitBlockingResponse() marked
blockingResponseInitiated = true immediately after scheduling the
off-event-loop commitBlockingResponse() call, without waiting for it
to actually run. If that async commit failed once executed, the
failure was silently swallowed and every later tryBlock() call for
the same request would short-circuit to true, hiding the failure
from block_failure telemetry. The flag is now set only inside the
scheduled task, after commitBlockingResponse() actually returns true,
matching the same-thread branch's existing behavior.

Author: jandro996

dd-java-agent/instrumentation/netty/netty-4.1/src/main/java/datadog/trace/instrumentation/netty41/server/NettyHttpServerDecorator.java

@@ -164,10 +164,12 @@ public boolean tryCommitBlockingResponse(
             .channel()
             .eventLoop()
             .execute(
-                () ->
-                    commitBlockingResponse(
-                        segment, statusCode, templateType, extraHeaders, securityResponseId));
-        blockingResponseInitiated = true;
+                () -> {
+                  if (commitBlockingResponse(
+                      segment, statusCode, templateType, extraHeaders, securityResponseId)) {
+                    blockingResponseInitiated = true;
+                  }
+                });
         return true;
       } catch (RuntimeException rte) {
         log.warn("Failed scheduling blocking handler", rte);