Update Changelog for 1.39.13 release #509

Job	Run time
Test (ubuntu-20.04, OmniSharp.MSBuild.Tests,OmniSharp.Roslyn.CSharp.Tests,OmniSharp.DotNetTest.Te...	14m 30s
Test (ubuntu-20.04, OmniSharp.Lsp.Tests,OmniSharp.Script.Tests,OmniSharp.Tests,OmniSharp.Stdio.Te...	8m 18s
Test (windows-2022, OmniSharp.MSBuild.Tests,OmniSharp.Roslyn.CSharp.Tests,OmniSharp.DotNetTest.Te...	19m 59s
Test (windows-2022, OmniSharp.Lsp.Tests,OmniSharp.Script.Tests,OmniSharp.Tests,OmniSharp.Stdio.Te...	13m 35s
Test (macos-13, OmniSharp.MSBuild.Tests,OmniSharp.Roslyn.CSharp.Tests,OmniSharp.DotNetTest.Tests,...	22m 51s
Test (macos-13, OmniSharp.Lsp.Tests,OmniSharp.Script.Tests,OmniSharp.Tests,OmniSharp.Stdio.Tests,...	13m 58s
	1h 33m 11s

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