Update post-build.yml to pass path to SignCheckExclusionsFile

[JohnTortugo]

Need to add this to pass the parameter to the signing validation step so that users can inform files that should be excluded from signing validation.

Test build is running here: https://dnceng.visualstudio.com/internal/_build/results?buildId=295740&view=results

[AaronRobinsonMSFT]

@JohnTortugo I am actually changing my mind here. Why is the extension here .props? The SignCheck tool's exclusion list seems to be a flat text file rather than an MSBuild file.

arcade/src/SignCheck/Microsoft.SignCheck/Verification/Exclusions.cs

Lines 35 to 53 in 44ccf0f

	public Exclusions(string path)
	{
	if (File.Exists(path))
	{
	using (StreamReader fileReader = File.OpenText(path))
	{
	string line = fileReader.ReadLine();
	while (line != null)
	{
	if (!String.IsNullOrEmpty(line))
	{
	Add(new Exclusion(line));
	}
	line = fileReader.ReadLine();
	}
	}
	}
	}