update assembly reference snapshots

Author: lucaspimentel

tracer/test/Datadog.Trace.Tests/Snapshots/PublicApiTests.Datadog.Trace.AssemblyReferencesHaveNotChanged.net6.0.verified.txt

@@ -9,6 +9,7 @@ Microsoft.Net.Http.Headers, Version=2.0.0.0, Culture=neutral, PublicKeyToken=adb
 Microsoft.Win32.Primitives, Version=6.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a
 System.Collections, Version=6.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a
 System.Collections.Concurrent, Version=6.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a
+System.Collections.Immutable, Version=6.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a
 System.Collections.NonGeneric, Version=6.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a
 System.Collections.Specialized, Version=6.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a
 System.ComponentModel.Primitives, Version=6.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a

tracer/test/Datadog.Trace.Tests/Snapshots/PublicApiTests.Datadog.Trace.AssemblyReferencesHaveNotChanged.netcoreapp3.1.verified.txt

@@ -10,6 +10,7 @@ Microsoft.Win32.Primitives, Version=4.1.2.0, Culture=neutral, PublicKeyToken=b03
 System.Buffers, Version=4.0.2.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51
 System.Collections, Version=4.1.2.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a
 System.Collections.Concurrent, Version=4.0.15.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a
+System.Collections.Immutable, Version=1.2.5.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a
 System.Collections.NonGeneric, Version=4.1.2.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a
 System.Collections.Specialized, Version=4.1.2.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a
 System.ComponentModel.Primitives, Version=4.2.2.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a