Run the VerifyDotnetFolderContents test on all images

[lbussell]

The VerifyDotnetFolderContents test currently has incorrect conditions that may be causing it to not run on the majority of Linux platforms:

dotnet-docker/tests/Microsoft.DotNet.Docker.Tests/SdkImageTests.cs

Lines 137 to 153 in e025c25

	if (!IsPowerShellSupported(imageData, out string powerShellReason))
	{
	OutputHelper.WriteLine(powerShellReason);
	return;
	}
	// Skip test on CBL-Mariner. Since installation is done via RPM package, we just need to verify the package installation
	// was done (handled by VerifyPackageInstallation test). There's no need to check the actual contents of the package.
	if (imageData.OS.Contains("cbl-mariner"))
	{
	return;
	}
	if (!imageData.SdkOS.StartsWith(OS.Alpine) && DockerHelper.IsLinuxContainerModeEnabled)
	{
	return;
	}

In particular, Mariner hasn't relied on RPM installs since 6.0, and the !imageData.SdkOS.StartsWith(OS.Alpine) && DockerHelper.IsLinuxContainerModeEnabled condition seems completely incorrect. We should re-evaluate which platforms this test can be ran on and run it on as many as possible.

We should also run the test on (potentially) distroless images and platforms that don't support PowerShell.