Replace TarFileMode with UnixFileMode

[carlossanlop]

Replaces the System.Formats.Tar.TarFileMode enum originally added in this PR: #67883
With the more general one, System.IO.UnixFileMode, which was freshly added in this PR: #69980

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Issue Details

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Replaces the System.Formats.Tar.TarFileMode enum originally added in this PR: #67883
With the more general one, System.IO.UnixFileMode, which was freshly added in this PR: #69980

Author:	carlossanlop
Assignees:	carlossanlop
Labels:	area-System.IO
Milestone:	7.0.0

[carlossanlop]

@baronfel FYI

[baronfel]

Lovely, thank you for the ping. @rainersigwald this may be relevant.

[eerhardt]

[carlossanlop]

Test failures unrelated:

#70450 System.IO.Tests.SymbolicLink_Changed_Tests.FileSystemWatcher_SymbolicLink_IncludeSubdirectories_DoNotDereferenceChildLink
#71233 System.Net.Http.Functional.Tests - Assertion Failed - ClientCertificates. Expected enumerable cloned value.
#70969 The process cannot access the file 'D:\a_work\1\s\artifacts\log\Release\Microsoft.NET.HostModel.ComHost.Tests_net7.0_x64.log' because it is being used by another process.