ci: add usethis to update-cdisc-data workflow extra-packages

The scheduled update workflow was failing with:
  Error in loadNamespace(x) : there is no package called 'usethis'

fetch_ct_sdtm.R, fetch_ct_adam.R, and build_catalogue.R all call
usethis::use_data() but usethis was not installed by the workflow.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: billdenney

.github/workflows/update-cdisc-data.yaml

@@ -32,7 +32,7 @@ jobs:
 
       - uses: r-lib/actions/setup-r-dependencies@v2
         with:
-          extra-packages: any::xml2
+          extra-packages: any::xml2, any::usethis
           needs: website
 
       - name: Run data fetch scripts