[DOC] Added File::FNM_SYSCASE example [Bug #16391] [ci skip]

dir.c

@@ -3176,6 +3176,7 @@ fnmatch_brace(const char *pattern, VALUE val, void *enc)
  *
  *     File.fnmatch('cat', 'CAT')                     #=> false # case sensitive
  *     File.fnmatch('cat', 'CAT', File::FNM_CASEFOLD) #=> true  # case insensitive
+ *     File.fnmatch('cat', 'CAT', File::FNM_SYSCASE)  #=> true or false # depends on the system default
  *
  *     File.fnmatch('?',   '/', File::FNM_PATHNAME)  #=> false # wildcard doesn't match '/' on FNM_PATHNAME
  *     File.fnmatch('*',   '/', File::FNM_PATHNAME)  #=> false # ditto