XML-module does not get indexed by DNN search

## Describe the bug
A feed does not seem to get indexed by DNN search.

## To Reproduce
Steps to reproduce the behavior:
1. Go to 'Edit Module Configuration'
2. Open 'Advanced Options'
3. Scroll down to 'Allow Indexing' and select 'always'
4. Save
5. The page is indexed
6. the xml-module is added to the search results scope
7. DNN 10.3.3, XML-module 6.0.5

## Expected behavior
After reindexing, the contents should have been reindexed, but it's not

## Error log
No errors in the error log

Is there a workaround? Or any other solution?

Reproduce the issue with DNN 10.3.3 and XML-module 6.0.5 by enabling “always” indexing in Edit Module Configuration, reindexing, and checking the search results scope. Trace the XML module’s indexing behavior and compare it with the expected result that the feed contents appear in DNN search without an error log.

Written by the indexing model from the issue text.