Update ActiveIssue URLs for Newtonsoft tests for immutable collections

[layomia]

Fixes https://github.com/dotnet/corefx/issues/36643#issuecomment-577501482

• Support for ImmutableArray<T> was added in Add support for immutable array corefx#39493
• Support for immutable dictionaries was added in Add support for immutable dictionaries corefx#37710
  • Dictionaries with non-string keys are not supported, so the active issue URLs for these tests were replaced with issues to the tracking issue for that feature.

Further tests for immutable collections:

• dictionaries: https://github.com/dotnet/runtime/blob/10717887317beb824e57cdb29417663615211e99/src/libraries/System.Text.Json/tests/Serialization/DictionaryTests.cs
• non-dictionaries:
  • https://github.com/dotnet/runtime/blob/10717887317beb824e57cdb29417663615211e99/src/libraries/System.Text.Json/tests/Serialization/Value.ReadTests.ImmutableCollections.cs
  • https://github.com/dotnet/runtime/blob/10717887317beb824e57cdb29417663615211e99/src/libraries/System.Text.Json/tests/Serialization/Value.WriteTests.ImmutableCollections.cs

cc @stephentoub

[stephentoub]

Thanks.