Description of the problem / feature request:

Version 2.4.0 breaks support for custom Javadoc tags.

For some of my Java projects, I'm using Maven's Javadoc Plugin to create Custom Javadoc Tags,
Mostly I use it for a @todo tag as described in the link.
Later in the project's life cycle, I use this tag to build reports and open issues.

When using Error Prone version before 2.4.0, e.g. 2.3.4, this works well.
Bumping to 2.4.0 makes the use of this tag a violation:

MyFile.java:[95,5] [InvalidBlockTag] Tag name `todo` is unknown. Did you mean tag `see`?

Feature requests: what underlying problem are you trying to solve with this feature?

I'm trying to get Error Prone to work well with custom Javadoc tags.

Bugs: what's the simplest, easiest way to reproduce this bug? Please provide a minimal example if possible.

Adding an unknown tag to a code comment should do the trick.

What version of Error Prone are you using?

With version 2.3.4 - this works well, custom Javadoc tags do not count as a violation.
With version 2.4.0 - this breaks, the custom Javadoc tag is considered a violation.

Have you found anything relevant by searching the web?

I've found this issue: 1796.
That might slightly resemble my issue.

The difference is, the other issue discusses three specific tags,
@apiNote, @implSpec, and @implNote which to my understanding are new to Java.
My issue discusses custom tags in general, although the tag in question is a @todo tag.