Fix pkgdown build

[yutannihilation]

This pull request is an attempt to fix this failure on CI.

https://github.com/r-lib/ragg/actions/runs/13788588896/job/38562367647#step:6:303

 ✖ Reference metadata not ok.
  In _pkgdown.yml, 1 topic missing from index: "agg_record".
  Either use `@keywords internal` to drop from index, or

[thomasp85]

thanks :-)