ddl: fast fail check for create index to accelerate CI (#8592)
ddl: fast fail check for create index to accelerate CI (#8592)

➜  session git:(master) ✗ GO111MODULE=on go test  -check.f TestIndexMaxLength
before:
ok  	github.com/pingcap/tidb/session	18.229s
after:
ok  	github.com/pingcap/tidb/session	0.146s
pingcap/tidb,ngaut/tidb,ming-relax/tidb,c4pt0r/tidb,pingcap/tidb,c4pt0r/tidb,kyle-wang/tidb,kyle-wang/tidb,c4pt0r/tidb,ming-relax/tidb,ngaut/tidb,pingcap/tidb,qiuyesuifeng/tidb,XuHuaiyu/tidb,cosmtrek/tidb,Cofyc/tidb,coocood/tidb,c4pt0r/tidb,ngaut/tidb,kyle-wang/tidb,kyle-wang/tidb,coocood/tidb,pingcap/tidb,Cofyc/tidb,kyle-wang/tidb,ngaut/tidb,kyle-wang/tidb,pingcap/tidb,XuHuaiyu/tidb,EvilMcJerkface/tidb,c4pt0r/tidb,ngaut/tidb,pingcap/tidb,c4pt0r/tidb,cosmtrek/tidb,EvilMcJerkface/tidb,ngaut/tidb,qiuyesuifeng/tidb