chore(ci): bump crossref-tags baseline retention to 30 days

PRs that sit idle for a week or two should still find a baseline at
their merge-base SHA. With 5-day retention they'd fall back to
"changed-files only" rendering (which fires on every cross-reference
tag in any touched file — noisy on maintenance PRs).

Baseline is ~55 KB per master push, so 30 days of retention is trivial.

Author: kim-em

.github/workflows/build_template.yml

@@ -760,7 +760,10 @@ jobs:
         with:
           name: crossref-tags-baseline
           path: crossref-tags.tsv
-          retention-days: 5
+          # 30 days: PRs that sit idle for a week or two should still find a
+          # baseline at their merge-base SHA. The TSV is ~55 KB so the
+          # storage cost is trivial.
+          retention-days: 30
 
       - name: prepare crossref bridge outputs
         # The privileged crossref_review.yml workflow_run job only fires