update swagger pareer to 2.1.28 (#21325) #173

Job	Run time
Build .Net projects (samples/client/petstore/csharp/generichost/net4.7/AnyOf)	1m 24s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.7/OneOf)	1m 4s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.7/FormModels)	1m 11s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.7/Petstore)	1m 3s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.7/AnyOfNoCompare)	1m 5s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.7/AllOf)	1m 28s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.8/FormModels)	1m 2s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.8/AnyOfNoCompare)	1m 54s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.8/OneOf)	1m 6s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.8/AnyOf)	2m 17s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.8/AllOf)	1m 3s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.7/UseDateTimeForDate)	1m 18s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.8/Petstore)	1m 42s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.8/UseDateTimeForDate)	1m 1s
	18m 38s

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