Replace Ubuntu 18 images with Ubuntu 20 in ARM 64 runs

[rzikm]

Closes #103354.

TLS resumption does not work reliably with the OpenSSL version present on Ubuntu 18.04 distribution. Since the distro in question is past EOL, we should simply update the queues to more recent distro image.

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[wfurt]

we should not be running on EOS system, right? If anything I feel we should update the run queue(s).

[rzikm]

we should not be running on EOS system, right? If anything I feel we should update the run queue(s).

Right, I see 18.04 has already been replaced with newer OSes on other platforms, so I changed this PR to update the queues to 20.04 images instead.

[rzikm]

Test failures are related

    System.Net.Quic.Tests.MsQuicPlatformDetectionTests.SupportedLinuxPlatforms_IsSupportedIsTrue [FAIL]
      Assert.True() Failure
      Expected: True
      Actual:   False
      Stack Trace:
        /_/src/libraries/System.Net.Quic/tests/FunctionalTests/MsQuicPlatformDetectionTests.cs(69,0): at System.Net.Quic.Tests.MsQuicPlatformDetectionTests.SupportedLinuxPlatforms_IsSupportedIsTrue()
           at System.RuntimeMethodHandle.InvokeMethod(Object target, Void** arguments, Signature sig, Boolean isConstructor)
        /_/src/coreclr/System.Private.CoreLib/src/System/Reflection/MethodBaseInvoker.CoreCLR.cs(36,0): at System.Reflection.MethodBaseInvoker.InterpretedInvoke_Method(Object obj, IntPtr* args)
        /_/src/libraries/System.Private.CoreLib/src/System/Reflection/MethodBaseInvoker.cs(57,0): at System.Reflection.MethodBaseInvoker.InvokeWithNoArgs(Object obj, BindingFlags invokeAttr)
      Output:
        Running on Distro=ubuntu VersionId=20.4
    System.Net.Quic.Tests.MsQuicPlatformDetectionTests.UnsupportedPlatforms_ThrowsPlatformNotSupportedException [PASS]
      Output:
        System.Net.Quic is not supported on this platform: Unable to load MsQuic library version '2'. For more information see: 

The image is missing MsQuic, we will need to update the image before merging this PR

edit, actually we might want to update to 22.04, since that image already contains MsQuic.

[rzikm]

/ba-g None of the failures are on the new platform or the test in question.