DM: update DM mydumper extra-args example config (#21421)

Author: JQWong7

dm/dm-precheck.md

@@ -176,7 +176,7 @@ mydumpers:                           # Configuration arguments of the dump proce
   global:                            # Configuration name
     threads: 4                       # The number of threads that access the upstream when the dump processing unit performs the precheck and exports data from the upstream database (4 by default)
     chunk-filesize: 64               # The size of the files generated by the dump processing unit (64 MB by default)
-    extra-args: "--consistency none" # Other arguments of the dump processing unit. You do not need to manually configure table-list in `extra-args`, because it is automatically generated by DM.
+    extra-args: "--consistency auto" # Other arguments of the dump processing unit. You do not need to manually configure table-list in `extra-args`, because it is automatically generated by DM.
 
 ```
 

dm/task-configuration-file-full.md

@@ -114,7 +114,7 @@ mydumpers:
   global:                            # The configuration name of the processing unit.
     threads: 4                       # The number of threads that access the upstream when the dump processing unit performs the precheck and exports data from the upstream database (4 by default)
     chunk-filesize: 64               # The size of the file generated by the dump processing unit (64 MB by default).
-    extra-args: "--consistency none" # Other arguments of the dump processing unit. You do not need to manually configure table-list in `extra-args`, because it is automatically generated by DM.
+    extra-args: "--consistency auto" # Other arguments of the dump processing unit. You do not need to manually configure table-list in `extra-args`, because it is automatically generated by DM.
 
 # Configuration arguments of the load processing unit.
 loaders: