Transform CVE feed shortcode compliance check to warning

Previously it would cause the build to fail, which could lead to
confusing situation since the CVE feed comes from outside of the website
and could break the workflow. See related discussion:
#38579 (comment)

layouts/shortcodes/cve-feed.html

@@ -1,6 +1,6 @@
 {{ $feed := getJSON .Site.Params.cveFeedBucket }}
 {{ if ne $feed.version "https://jsonfeed.org/version/1.1" }}
-  {{ errorf "Build Failed. CVE feed does not comply with JSON feed v1.1" }}
+  {{ warnf "CVE feed shortcode. KEP-3203: CVE feed does not comply with JSON feed v1.1." }}
 {{ end }}
 <table class="security-cves">
   <caption style="caption-side: top;">{{ T "cve_table" }} {{ printf (T "cve_table_date_format_string") ($feed._kubernetes_io.updated_at | time.Format (T "cve_table_date_format")) }}</caption>