Fix and enable tests in CI for Linux

[GerardSmit]

While working on #85, I've ran the tests on Linux to validate my changes work on both Windows and Linux, however on Linux the tests are failing:

Failed!  - Failed:    13, Passed:   415, Skipped:     0, Total:   428, Duration: 2 s - Zio.Tests.dll (net8.0)

The following tests are failing:

[xUnit.net 00:00:00.44]     Zio.Tests.FileSystems.TestPhysicalFileSystemCompat.TestDirectoryDeleteAndOpenFile [FAIL]
[xUnit.net 00:00:00.57]     Zio.Tests.FileSystems.TestPhysicalFileSystem.TestFile [FAIL]
[xUnit.net 00:00:00.70]     Zio.Tests.FileSystems.TestZipArchiveFileSystem.TestCommonRead [FAIL]
[xUnit.net 00:00:00.71]     Zio.Tests.FileSystems.TestPhysicalFileSystem.TestDirectory [FAIL]
[xUnit.net 00:00:00.83]     Zio.Tests.FileSystems.TestSubFileSystem.TestBasic [FAIL]
[xUnit.net 00:00:00.91]     Zio.Tests.FileSystems.TestPhysicalFileSystem.TestFileExceptions [FAIL]
[xUnit.net 00:00:01.10]     Zio.Tests.FileSystems.TestPhysicalFileSystem.TestCommonRead [FAIL]
[xUnit.net 00:00:01.35]     Zio.Tests.FileSystems.TestPhysicalFileSystem.TestDirectoryExceptions [FAIL]
[xUnit.net 00:00:01.37]     Zio.Tests.FileSystems.TestPhysicalFileSystemCompat.TestDirectoryExceptions [FAIL]
[xUnit.net 00:00:01.73]     Zio.Tests.FileSystems.TestPhysicalFileSystem.TestEnumerate [FAIL]
[xUnit.net 00:00:01.76]     Zio.Tests.FileSystems.TestPhysicalFileSystemCompat.TestFile [FAIL]
[xUnit.net 00:00:01.79]     Zio.Tests.FileSystems.TestPhysicalFileSystem.TestFileSystemInvalidDriveLetter [FAIL]
[xUnit.net 00:00:02.35]     Zio.Tests.FileSystems.TestPhysicalFileSystemCompat.TestFileExceptions [FAIL]

GitHub Actions doesn't catch this because the CI only runs on Windows:

zio/.github/workflows/ci.yml

Line 14 in c23f0a0

runs-on: windows-latest

[xoofx]

Yeah, I didn't bother in the past to make them compatible. I agree that it would be nice. I have actually started to run many of my CI on Ubuntu to speed up CI spin up. PR welcome if you have the courage. ☺️