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

This PR was merged into the 5.4 branch. Discussion ---------- [Cache] Update external link Updated link for Ryan Tomayko's article "Things Caches Do" <!-- If your pull request fixes a BUG, use the oldest maintained branch that contains the bug (see https://symfony.com/releases for the list of maintained branches). If your pull request documents a NEW FEATURE, use the same Symfony branch where the feature was introduced (and `6.x` for features of unreleased versions). --> Commits ------- 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