Use Canonical-published checksums for installing Chisel tool

[lbussell]

Currently in update-dependencies, we manually calculate checksums for Chisel:

dotnet-docker/eng/update-dependencies/ChiselUpdater.cs

Lines 50 to 59 in 6ffe4d9

	protected override string? GetValue()
	{
	string? downloadUrl = base.GetValue();
	if (downloadUrl is null)
	{
	return null;
	}
	return ChecksumHelper.ComputeChecksumShaAsync(s_httpClient, downloadUrl).Result;
	}

For future releases, Canonical will compute and publish their own checksums. We should use those once they're available:

• chore: publish release checksums canonical/chisel#155