Ungrouping and re-saving included workflows can crash with a file access exception

[glopesdev]

To reproduce:

1. Create or load an include workflow in the Extensions folder
2. Ungroup the included workflow and re-save it over the same file

Note the issue is more reproducible running a debug build inside VS but can still happen when running outside with a much lower probability.

The problem seems to be connected with the fix in #1134 where a read-only stream is opened on the workflow file for upgrade but never explicitly closed. Apparently wrapping the stream in a XmlReader class and disposing it is not sufficient for closing the original stream.

bonsai/Bonsai.Editor/GraphModel/UpgradeHelper.cs

Lines 89 to 95 in 809d199

	Stream workflowStream;
	try { workflowStream = GetWorkflowStream(fileName); }
	catch (SystemException) { workflowStream = null; }
	if (workflowStream != null)
	{
	using var reader = XmlReader.Create(workflowStream);