System data definition is different from swagger

[tadelesh]

TypeSpec definition for createdAt:

typespec-azure/packages/typespec-azure-resource-manager/lib/common-types/types.tsp

Line 347 in daa3b15

createdAt?: plainDate;

Swagger definition: https://github.com/Azure/azure-rest-api-specs/blob/b5512186602fbe490d273aab7ebddc21f8e7f855/specification/common-types/resource-management/v5/types.json#L527

[markcowl]

Closing in favor of: #377

[tadelesh]

cc: @allenjzhang

[pshao25]

I suppose the expected type is utcDateTime? BTW, the document is different too. We should make them same too.

[allenjzhang]

fixed in pending PR #945