mass replace "flip map -> foreach"

See `foreach`-introduction commit.
```
rg 'flip map ' --files-with-matches | xargs sed -i 's/flip map /foreach /g'
```

nixos/modules/services/networking/ssh/sshd.nix

@@ -502,7 +502,7 @@ in
 
     assertions = [{ assertion = if cfg.forwardX11 then cfgc.setXAuthLocation else true;
                     message = "cannot enable X11 forwarding without setting xauth location";}]
-      ++ flip map cfg.listenAddresses ({ addr, ... }: {
+      ++ foreach cfg.listenAddresses ({ addr, ... }: {
         assertion = addr != null;
         message = "addr must be specified in each listenAddresses entry";
       });