minor #18202 [Cache] Update external link (aurac)

This PR was merged into the 5.4 branch.

Discussion
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[Cache] Update external link

Updated link for Ryan Tomayko's article "Things Caches Do"

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Commits
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2ef7004 Update external link

Author: OskarStark

http_cache.rst

@@ -372,7 +372,7 @@ Learn more
 
     http_cache/*
 
-.. _`Things Caches Do`: https://2ndscale.com/writings/things-caches-do
+.. _`Things Caches Do`: https://tomayko.com/blog/2008/things-caches-do
 .. _`Cache Tutorial`: https://www.mnot.net/cache_docs/
 .. _`Varnish`: https://varnish-cache.org/
 .. _`Squid in reverse proxy mode`: https://wiki.squid-cache.org/SquidFaq/ReverseProxy