Footnotes: footnotes within nested blocks are sometimes counted twice

[andrewserong]

Following on from #52682, it looks like there's still an issue with footnotes sometimes being counted multiple times. It's a bit edge-casey, but I believe a reliable way to reproduce the issue is:

1. Add a Group block to a post
2. Add a Quote block within the Group block
3. Add a footnote to the paragraph within the Quote block as well as to the Citation of the Quote block
4. Notice that the footnote item is duplicated and synced twice:

2023-07-27.16.39.31.mp4

From looking at #52682, I think this might be a result of iterating over inner blocks as well addValuesForBlocks being called a second time for blocks with InnerBlocks.Content? CC: @ellatrix, @mcsf, @ramonjd, @tellthemachines

[ellatrix]

It seems to be the citation that is the problem. Adding footnotes to the paragraph seems to work fine