Use $URL not $DEPLOY_PRIME_URL for prod deploys

$DEPLOY_PRIME_URL appears to point at a .netlify.app version of the
site, rather than the URL it's actually getting deployed as for prod
deploys. But is needed for preview deploys.

tooling/common-config/deploy-netlify.sh

@@ -4,5 +4,10 @@ set -euo pipefail
 
 npm install --legacy-peer-deps
 
+URL_TO_USE="${URL}"
+if [[ "${PULL_REQUEST}" == "true" ]]; then
+  URL_TO_USE="${DEPLOY_PRIME_URL}"
+fi
+
 # We set --baseURL on netlify so that any references to .Permalink end up pointing at deploy preview pages, rather than being hard-coded to point at the production URLs.
-hugo --minify --environment production --baseURL $DEPLOY_PRIME_URL && npx pagefind --site "public"
+hugo --minify --environment production --baseURL "${URL_TO_USE}" && npx pagefind --site "public"