Link checker fails when anchor exists

[bmorelli25]

Summary

I'm struggling to figure out why this is the case, but I'm seeing ~70 instances of this.

Reproduce:

1. Clone the elasticsearch.md repo
2. cd elasticsearch.md
3. Add two files:
   a. add-missing-anchors.py https://gist.github.com/bmorelli25/bc93ab7dd4d4e89270133a4cc5d27a4b
   b. output.log.txt https://gist.github.com/bmorelli25/c8d46c59074f652e6cc412e38b9d8f7f (the docs-builder error log when building the elasticsearch.md content set)
4. Run python add-missing-anchors.py ./docs/ (this will use the error log to add missing anchors to all files)
5. Run docs-builder: dotnet publish "src/docs-builder/docs-builder.csproj" && ./.artifacts/publish/docs-builder/release/docs-builder -p ../elasticsearch.md.

Even though all anchors are now present, the docs build fails with ~70 broken links. Partial error log:

:: fail: Documentation.Builder.Log[0] `forced-awareness` does not exist in shard-allocation-awareness.md. (/Users/brandon/Documents/GitHub/elasticsearch.md/docs/modules-cluster.md:209)

:: fail: Documentation.Builder.Log[0] `data-node-role` does not exist in node-roles-overview.md. (/Users/brandon/Documents/GitHub/elasticsearch.md/docs/modules-cluster.md:266)
:: fail: Documentation.Builder.Log[0] `data-node-role` does not exist in node-roles-overview.md. (/Users/brandon/Documents/GitHub/elasticsearch.md/docs/modules-cluster.md:266)
:: fail: Documentation.Builder.Log[0] `data-node-role` does not exist in node-roles-overview.md. (/Users/brandon/Documents/GitHub/elasticsearch.md/docs/high-availability-cluster-small-clusters.md:53)
:: fail: Documentation.Builder.Log[0] `ml-node-role` does not exist in node-roles-overview.md. (/Users/brandon/Documents/GitHub/elasticsearch.md/docs/high-availability-cluster-small-clusters.md:53)
:: fail: Documentation.Builder.Log[0] `voting-only-node` does not exist in node-roles-overview.md. (/Users/brandon/Documents/GitHub/elasticsearch.md/docs/high-availability-cluster-small-clusters.md:57)

:: fail: Documentation.Builder.Log[0] `schedule-cron` does not exist in . (/Users/brandon/Documents/GitHub/elasticsearch.md/docs/snapshot-settings.md:19)

:: fail: Documentation.Builder.Log[0] `shard-recovery` does not exist in shard-allocation-relocation-recovery.md. (/Users/brandon/Documents/GitHub/elasticsearch.md/docs/high-availability-cluster-design-large-clusters.md:7)

If you go through the files listed in the log, you'll see that the anchor does exist in all markdown files. If you build with the serve command, all of these links also work.

Other note: Some errors don't list a file name:

:: fail: Documentation.Builder.Log[0] `schedule-cron` does not exist in . (/Users/brandon/Documents/GitHub/elasticsearch.md/docs/snapshot-settings.md:19)

This seems to occur when the file name starts with an underscore (_). In the example above, the file name is: _schedule_types.md.

[bmorelli25]

This is happening because of this line in the TOC file:

exclude:
  - '_*.md'

This is preventing any _* file names from being included in the TOC, even though they are specified below this line in docset.yml.