Updated go mod for search fixes

[kristin-kronstain-brown]

Bumps docs-theme-extras to v0.3.17-beta.1 (solo-io/docs-theme-extras#64):

• Search: sites with many version trees no longer freeze the page and then show "No results found". Results don't pop open after you click away while the index loads, and multi-word queries no longer stall the page.
• Navbar dropdowns: keyboard focus opens them, Escape closes them, and a mouse click no longer pins them open.
• Mobile drawer: after you switch docTabs, screen readers announce the tree that is shown instead of an empty drawer.
• Landmarks: the navbar and sidebar <nav> elements have labels, in English and Japanese.

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