docs: fix broken global policy card rendering on policy page

[anvithagowda098]

Description

Motivation: The "Global policy attachment" card in the Policy behavior section was rendering as raw HTML on the live site instead of as a styled card, visible to all users at /docs/envoy/latest/about/policies/.

What changed: Fixed by wrapping the entire {{< cards >}} block inside the {{< version exclude-if="2.0.x" >}} shortcode instead of nesting version inside cards. This is the same pattern already used in the Policy CRDs section directly above on the same page.

/kind fix

Changelog

Fixed raw HTML rendering of the Global policy attachment card in the Policy behavior section on the Policies landing page.

Additional Notes

• The 2.0.x version correctly shows nothing under Policy behavior. Neither card existed in that version, and the maintainer confirmed that 2.0.x docs will be removed entirely soon.
• The include-if parameter of the {{< version >}} shortcode is currently non-functional (checks page front matter instead of shortcode params). This is a separate issue and not addressed in this PR.