`text and `json` formats for a tag does not work correctly.

[Carrotman42]

Reproduction steps:

1. Open https://gerrit.googlesource.com/gitiles/+/refs/tags/v1.1.0
2. Scroll to bottom of page, click json link at bottom right of page (link)
3. Observe INVALID_ARGUMENT error loading result, along with additional messages "The specified object's type is not supported" and the like. (I am getting an internal stacktrace that I don't want to share publically, which is why I haven't just pasted the whole thing.)
4. (trying text doesn't work either)

Note that the same works if you are using the commit ID instead, which loads a slightly different page since it doesn't have the tag information included.