minor #21234 Typo s/sytsem/system (PhilETaylor)

This PR was merged into the 7.3 branch.

Discussion
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Typo s/sytsem/system

Simple typo fix

Commits
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d50c1d4 s/sytsem/system

Author: OskarStark

reference/configuration/doctrine.rst

@@ -353,7 +353,7 @@ to cache each of Doctrine ORM elements (queries, results, etc.):
                     ->pool('doctrine.result_cache_pool')
                         ->adapters('cache.app')
                     ->pool('doctrine.system_cache_pool')
-                        ->adapters('cache.sytsem');
+                        ->adapters('cache.system');
 
             $doctrine->orm()
                 // ...