[fix](cancel) Fix cancel failure (#48751)

### What problem does this PR solve?

If a query is canceled before fragment contexts are prepared, no
fragment context will be found. So we should set execution ready to
ensure tasks will not be blocked.

be/src/pipeline/pipeline_x/pipeline_x_task.h

@@ -139,7 +139,6 @@ class PipelineXTask : public PipelineTask {
     int task_id() const { return _index; };
 
     void clear_blocking_state() override {
-        _state->get_query_ctx()->get_execution_dependency()->set_always_ready();
         // We use a lock to assure all dependencies are not deconstructed here.
         std::unique_lock<std::mutex> lc(_dependency_lock);
         if (!_finished) {

be/src/runtime/query_context.cpp

@@ -250,6 +250,7 @@ void QueryContext::cancel(std::string msg, Status new_status, int fragment_id) {
 
 void QueryContext::cancel_all_pipeline_context(const PPlanFragmentCancelReason& reason,
                                                const std::string& msg) {
+    set_execution_dependency_ready();
     std::vector<std::weak_ptr<pipeline::PipelineFragmentContext>> ctx_to_cancel;
     {
         std::lock_guard<std::mutex> lock(_pipeline_map_write_lock);
@@ -267,6 +268,7 @@ void QueryContext::cancel_all_pipeline_context(const PPlanFragmentCancelReason&
 Status QueryContext::cancel_pipeline_context(const int fragment_id,
                                              const PPlanFragmentCancelReason& reason,
                                              const std::string& msg) {
+    set_execution_dependency_ready();
     std::weak_ptr<pipeline::PipelineFragmentContext> ctx_to_cancel;
     {
         std::lock_guard<std::mutex> lock(_pipeline_map_write_lock);