Fix ABI break introduced by commit 4daa140a2f.

Move the newly defined enum value REORDER_BUFFER_CHANGE_INTERNAL_SPEC_ABORT
at the end to avoid ABI break in the back branches. We need to back-patch
this till v11 because before that it is already at the end.

Reported-by: Tomas Vondra
Backpatch-through: 11
Discussion: https://postgr.es/m/CAExHW5sPKF-Oovx_qZe4p5oM6Dvof7_P+XgsNAViug15Fm99jA@mail.gmail.com

src/include/replication/reorderbuffer.h

@@ -62,8 +62,8 @@ enum ReorderBufferChangeType
 	REORDER_BUFFER_CHANGE_INTERNAL_TUPLECID,
 	REORDER_BUFFER_CHANGE_INTERNAL_SPEC_INSERT,
 	REORDER_BUFFER_CHANGE_INTERNAL_SPEC_CONFIRM,
-	REORDER_BUFFER_CHANGE_INTERNAL_SPEC_ABORT,
-	REORDER_BUFFER_CHANGE_TRUNCATE
+	REORDER_BUFFER_CHANGE_TRUNCATE,
+	REORDER_BUFFER_CHANGE_INTERNAL_SPEC_ABORT
 };
 
 /* forward declaration */