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

test/integration/default/files/_mapdata/gentoo-2-sysd.yaml

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

test/integration/default/files/_mapdata/gentoo-2-sysv.yaml

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

test/salt/pillar/default.sls

   {%- endif %}
   {#- Need this on various platforms to avoid the `kitchen verify` failure as mentioned above; see: #}
   {#- * https://gitlab.com/saltstack-formulas/infrastructure/salt-image-builder/-/commit/cb6781a2bba9 #}
-  {%- if grains.os in ["Arch", "OpenBSD"] or grains.get("oscodename", "") in ["openSUSE Tumbleweed"] %}
+  {%- if grains.os in ["Arch", "OpenBSD", "Gentoo"] or grains.get("oscodename", "") in ["openSUSE Tumbleweed"] %}
   PubkeyAcceptedAlgorithms: "+ssh-rsa"
   {%- endif %}