[Docs] Fix minor paragraph indentation error for multiple Indices params (#25535)

Author: pmusa

docs/reference/api-conventions.asciidoc

@@ -47,7 +47,7 @@ to. If `open` is specified then the wildcard expression is expanded to only
 open indices and if `closed` is specified then the wildcard expression is
 expanded only to closed indices. Also both values (`open,closed`) can be
 specified to expand to all indices.
-
++
 If `none` is specified then wildcard expansion will be disabled and if `all`
 is specified, wildcard expressions will expand to all indices (this is equivalent
 to specifying `open,closed`).