Makefile: change test parallel to 8 (#12885)
Makefile: change test parallel to 8 (#12885)


c4pt0r/tidb,kyle-wang/tidb,c4pt0r/tidb,pingcap/tidb,pingcap/tidb,c4pt0r/tidb,EvilMcJerkface/tidb,ngaut/tidb,EvilMcJerkface/tidb,kyle-wang/tidb,kyle-wang/tidb,ngaut/tidb,c4pt0r/tidb,XuHuaiyu/tidb,ngaut/tidb,coocood/tidb,ngaut/tidb,Cofyc/tidb,pingcap/tidb,ming-relax/tidb,coocood/tidb,ngaut/tidb,kyle-wang/tidb,pingcap/tidb,pingcap/tidb,pingcap/tidb,c4pt0r/tidb,Cofyc/tidb,kyle-wang/tidb,XuHuaiyu/tidb,ming-relax/tidb,c4pt0r/tidb,ngaut/tidb,kyle-wang/tidb