Update system.md (#7965)

docs/en/query_language/system.md

@@ -3,7 +3,7 @@
 - [RELOAD DICTIONARIES](#query_language-system-reload-dictionaries)
 - [RELOAD DICTIONARY](#query_language-system-reload-dictionary)
 - [DROP DNS CACHE](#query_language-system-drop-dns-cache)
-- [DROP MARKS CACHE](#query_language-system-drop-marks-cache)
+- [DROP MARK CACHE](#query_language-system-drop-mark-cache)
 - [FLUSH LOGS](#query_language-system-flush_logs)
 - [RELOAD CONFIG](#query_language-system-reload-config)
 - [SHUTDOWN](#query_language-system-shutdown)
@@ -36,7 +36,7 @@ Resets ClickHouse's internal DNS cache. Sometimes (for old ClickHouse versions)
 
 For more convenient (automatic) cache management, see disable_internal_dns_cache, dns_cache_update_period parameters.
 
-## DROP MARKS CACHE {#query_language-system-drop-marks-cache}
+## DROP MARK CACHE {#query_language-system-drop-mark-cache}
 
 Resets the mark cache. Used in development of ClickHouse and performance tests.