Only retry failed pexpect tests under CI

A false negative while testing locally should be a rare thing, and individual
pexpect tests already take too long in case of a non-match making for a painful
edit-test loop.

tests/interactive.fish

@@ -64,10 +64,16 @@ if not python3 -c 'import pexpect'
 end
 for i in $pexpect_files_to_test
     if not test_pexpect_file $i
+        # Retry pexpect tests under CI twice, as they are timing-sensitive and CI resource
+        # contention can cause tests to spuriously fail.
+        if set -qx CI
             say yellow "Trying $i for a second time"
             if not test_pexpect_file $i
                 set failed $failed $i
             end
+        else
+            set failed $failed $i
+        end
     end
 end