[docs] fix vale version (#2400)

Author: odow

.github/workflows/documentation.yml

@@ -33,6 +33,8 @@ jobs:
           path: ${{ github.workspace }}/latex-debug-logs
       - uses: errata-ai/vale-action@reviewdog
         with:
+          # TODO(odow): at some point, update to vale@3
+          version: 2.30.0
           files: docs/src
           fail_on_error: true
           filter_mode: nofilter