minor #10708 Framework configuration > Cache pools > Fix FQCN (ruudk)

This PR was submitted for the 4.1 branch but it was merged into the 3.4 branch instead (closes #10708).

Discussion
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Framework configuration > Cache pools > Fix FQCN

Namespace was escaped so this fixes it.

Commits
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4beae61 Framework configuration > Cache pools > Fix FQCN

Author: javiereguiluz

reference/configuration/framework.rst

@@ -2072,7 +2072,7 @@ settings from the base pool as defaults.
 
 .. note::
 
-    Your service MUST implement the ``Psr\\Cache\\CacheItemPoolInterface`` interface.
+    Your service MUST implement the ``Psr\Cache\CacheItemPoolInterface`` interface.
 
 public
 """"""