test(pillar): add ssh-rsa Kitchen workaround on Arch Linux [skip ci]

Need this on Arch Linux to avoid the `kitchen verify` failure; see:

* https://gitlab.com/saltstack-formulas/infrastructure/salt-image-builder/-/commit/cb6781a2bba9

test/integration/default/files/_mapdata/arch-base-latest.yaml

@@ -180,6 +180,7 @@ values:
     AcceptEnv: LANG LC_*
     ChallengeResponseAuthentication: 'no'
     PrintMotd: 'no'
+    PubkeyAcceptedAlgorithms: "+ssh-rsa"
     Subsystem: sftp /usr/lib/openssh/sftp-server
     UsePAM: 'yes'
     X11Forwarding: 'yes'