fix CI by declaring $pure_symbol_horizontal_bar

tests/fish_title.test.fish

@@ -9,6 +9,8 @@ end
 
 test "fish_title: contains current directory and previous command"
     (
+        set pure_symbol_horizontal_bar '—'
+
         fish_title 'last-command' 
     ) = "directory: last-command — "
 end
@@ -21,20 +23,25 @@ end
 
 test "fish_title: contains current path without a previous command"
     (
+        set pure_symbol_horizontal_bar '—'
+
         fish_title
     ) = "/tmp/current/directory — "
 end
 
 test "fish_title: support fish 2.x"  # how to test $_ ?
     (
+        set pure_symbol_horizontal_bar '—'
+
         fish_title
     ) = "/tmp/current/directory — "
 end
 
 test "fish_title: support fish 3.x"
     (
-       function status; echo 'fishtape'; end  # mock: status current-command
-
+        function status; echo 'fishtape'; end  # mock: status current-command
+        set pure_symbol_horizontal_bar '—'
+
         fish_title
     ) = "/tmp/current/directory — fishtape"
 end