fix: prompt editor click to insert variable (#21470)

web/app/components/base/prompt-editor/plugins/component-picker-block/variable-option.tsx

       tabIndex={-1}
       ref={setRefElement}
       onMouseEnter={onMouseEnter}
+      onMouseDown={(e) => {
+        e.preventDefault()
+        e.stopPropagation()
+      }}
       onClick={onClick}>
       <div className='mr-2'>
         {icon}