Merge branch '6.4' into 7.0

* 6.4:
  [Config] Prefixing FileExistenceResource::__toString() to avoid conflict with FileResource
  [String] Method toByteString conversion using iconv is unreachable
  [HttpKernel] Check controllers are allowed when using the fallback surrogate strategy
  [HttpKernel] Fix DebugLoggerConfigurator
  Set exception code to ldap error number
  Accept mixed key on DsPairStub
  check that the secret passed to RequestParser is not empty
  [HttpKernel] Fix PHP deprecation

Author: nicolas-grekas

Adapter/ExtLdap/Query.php

@@ -107,7 +107,7 @@ public function execute(): CollectionInterface
                         $this->resetPagination();
                     }
 
-                    throw new LdapException(sprintf('Could not complete search with dn "%s", query "%s" and filters "%s".%s.', $this->dn, $this->query, implode(',', $this->options['filter']), $ldapError));
+                    throw new LdapException(sprintf('Could not complete search with dn "%s", query "%s" and filters "%s".%s.', $this->dn, $this->query, implode(',', $this->options['filter']), $ldapError), $errno);
                 }
 
                 $this->results[] = $search;