[Docs] Fix typo in configuration.asciidoc (#28549)

Author: Cladis

docs/reference/setup/configuration.asciidoc

@@ -51,7 +51,7 @@ path.logs: /var/log/elasticsearch
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 [float]
-=== Environment variable subsitution
+=== Environment variable substitution
 
 Environment variables referenced with the `${...}` notation within the
 configuration file will be replaced with the value of the environment