[libraries][iOS][tvOS] Reenable System.Resource.ResourceManager and System.Collections.Immutable tests

[mdh1418]

Fixes #36876
Fixes #36893

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Issue Details

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Fixes #36876
Fixes #36893

Author:	mdh1418
Assignees:	-
Labels:	area-System.Resources
Milestone:	-

[mdh1418]

The failures in runtime-staging are unrelated
#57010, a flakey System.Diagnostics.DiagnosticSource.Tests, some System.TypeInitializationException : The type initializer for 'System.Drawing.Printing.PrintingServices' threw an exception.\n---- System.TypeInitializationException : The type initializer for 'System.Drawing.Printing.LibcupsNative' threw an exception.\n-------- System.PlatformNotSupportedException : System.Drawing.Common is not supported on non-Windows platforms. See https://aka.ms/systemdrawingnonwindows for more information., and a few System.NotSupportedException : Support for UTF-7 is disabled. See https://aka.ms/dotnet-warnings/SYSLIB0001 for more information.
Will create an issue targeting net 7.0 to skip the flakes

Checking the results of the build test runs, both System.Resources.Tests.ResourceManagerTests.GetString_FromTestClassWithoutNeutralResources and System.Resources.Tests.ResourceManagerTests.GetString_CultureFallback pass, and System.Collections.Immutable.Tests.ImmutableArrayTest.IStructuralEquatableGetHashCode has no member data, so it is not ran.