feat(ci): check for translation crashes

We have had issues in the past of translations causing crashes due to
malformed directives in .po files (e.g. unescaped '{').

Have CI check that such crashes don't happen (at least for documented
errors).

.github/workflows/check-error-docs.yml

@@ -28,8 +28,10 @@ jobs:
       - name: JS configure
         run: cd website && yarn install --production
 
-      - name: check
+      - name: check docs
         run: node website/check-error-documentation.mjs
+      - name: check diagnostics
+        run: node website/check-diagnostic-messages.mjs
 
 # quick-lint-js finds bugs in JavaScript programs.
 # Copyright (C) 2020  Matthew Glazar