Enable FAQPage schema on How to Test IaC guide (#20447)

Adds faq_schema: true to the front matter of
content/blog/how-to-test-infrastructure-as-code/index.md. The page
already has a genuine, well-formed FAQ section (10 real Q&A pairs
under '## Frequently asked questions', each a '### ...?' heading) but
was missing the opt-in flag that graph-builder.html checks before
invoking schema/collectors/faq-entity.html.

The page's schema_type: faq front-matter field is a decorative
editorial label only \u2014 it is never read by the schema partials, so it
was silently doing nothing for structured data. faq_schema: true is
the actual gating key (confirmed against
content/docs/iac/comparisons/terraform/_index.md, which already sets
it).

This is a single-line, opt-in-only change: no template or partial
changes, so pages that don't set faq_schema are unaffected.

Co-authored-by: workprentice <257153108+workprentice@users.noreply.github.com>

Author: workprentice[bot]

content/blog/how-to-test-infrastructure-as-code/index.md

@@ -11,6 +11,7 @@ tags:
     - testing
 category: best-practices
 schema_type: faq
+faq_schema: true
 aliases:
     - /what-is/how-to-step-up-cloud-infrastructure-testing/
 ---