ValidationRuleSet.Rules should be IEnumerable not IList

[baywet]

Not only this performs unnecessary allocs, it leads people to think they can do operations like clearing the list, which won't impact the source. This fix would represent a breaking change and needs to be addressed at part of the work for v2.

OpenAPI.NET/src/Microsoft.OpenApi/Validations/ValidationRuleSet.cs

Line 113 in 1a42bc4

public IList<ValidationRule> Rules