planner: add more unit tests for prepare plan cache (#28460)
planner: add more unit tests for prepare plan cache (#28460)

 
c4pt0r/tidb,ngaut/tidb,pingcap/tidb,c4pt0r/tidb,pingcap/tidb,ngaut/tidb,ngaut/tidb,kyle-wang/tidb,kyle-wang/tidb,kyle-wang/tidb,c4pt0r/tidb,pingcap/tidb,coocood/tidb,c4pt0r/tidb,kyle-wang/tidb,kyle-wang/tidb,pingcap/tidb,c4pt0r/tidb,coocood/tidb,ngaut/tidb,ngaut/tidb,pingcap/tidb,kyle-wang/tidb,c4pt0r/tidb,pingcap/tidb,ngaut/tidb