How to configure the index-files step?

**Description of the issue**

See `github/codeql-action/analyze` errors in https://github.com/microsoft/XmlNotepad/pull/122/checks?check_run_id=3265143671

I see it is using [codeql/csharp/tools/pre-finalize.cmd](https://github.com/github/codeql/blob/main/csharp/tools/pre-finalize.cmd) and I see this command is explicitly indexing xml files.

My solution contains bad xml files on purpose in a unit test project and so how do I configure this pre-finalize to ignore those files? Is there some magic I can put in a codeql-analysis.yml config file ?