update fish enabling script

Author: peterdragun

CHANGES.rst

@@ -7,6 +7,7 @@ Unreleased
 
 -   Fix issue with regex flags in shell completion. :issue:`2581`
 -   Bash version detection issues a warning instead of an error. :issue:`2574`
+-   Fix issue with completion script for Fish shell. :issue:`2567`
 
 
 Version 8.1.6

docs/shell-completion.rst

@@ -62,7 +62,7 @@ program name. This uses ``foo-bar`` as an example.
 
         .. code-block:: fish
 
-            eval (env _FOO_BAR_COMPLETE=fish_source foo-bar)
+            _FOO_BAR_COMPLETE=fish_source foo-bar | source
 
         This is the same file used for the activation script method
         below. For Fish it's probably always easier to use that method.