interactive tests: exit quietly if expect not available

It seems that 44cfe3e34 inadvertently included the requirement for the
expect tests to pass; revert this to its original sense.

tests/interactive.fish

@@ -39,7 +39,7 @@ cat interactive.config >>$XDG_CONFIG_HOME/fish/config.fish
 say -o cyan "Testing interactive functionality"
 if not type -q expect
     say red "Tests disabled: `expect` not found"
-    exit 1
+    exit 0
 end
 
 function test_file