Revert "feat(github-release): update k3s-io/k3s to v1.27.1+k3s1 (#710)" (#715)

This reverts commit 1080234b8a.

kubernetes/apps/system-upgrade/system-upgrade-controller/plans/agent.yaml

@@ -6,7 +6,7 @@ metadata:
   namespace: system-upgrade
 spec:
   # renovate: datasource=github-releases depName=k3s-io/k3s
-  version: "v1.27.1+k3s1"
+  version: "v1.26.3+k3s1"
   serviceAccountName: system-upgrade
   concurrency: 1
   nodeSelector:

kubernetes/apps/system-upgrade/system-upgrade-controller/plans/server.yaml

@@ -6,7 +6,7 @@ metadata:
   namespace: system-upgrade
 spec:
   # renovate: datasource=github-releases depName=k3s-io/k3s
-  version: "v1.27.1+k3s1"
+  version: "v1.26.3+k3s1"
   serviceAccountName: system-upgrade
   concurrency: 1
   cordon: true