Add GlobalEventExecutor#addTask to BlockHound exceptions. (#10262)

Motivation:

GlobalEventExecutor#addTask may be called during SingleThreadEventExecutor shutdown.
May result in a blocking call, because GlobalEventExecutor#taskQueue is a BlockingQueue.

Modifications:

Add allowBlockingCallsInside configuration for GlobalEventExecutor#addTask.

Result:

Fixes #10257.
When BlockHound is installed, GlobalEventExecutor#addTask is not reported as a blocking call.

common/src/main/java/io/netty/util/internal/Hidden.java

@@ -61,6 +61,8 @@ class Hidden {
                     "io.netty.util.concurrent.SingleThreadEventExecutor",
                     "confirmShutdown"
             );
+            builder.allowBlockingCallsInside("io.netty.util.concurrent.GlobalEventExecutor",
+                    "addTask");
 
             builder.allowBlockingCallsInside("io.netty.util.concurrent.GlobalEventExecutor",
                     "takeTask");