build: bump minimum Go version to 1.26.6

Containerd main now requires go 1.26.6 which breaks CI
when the installed Go toolchain (read from cri-tools go.mod)
is older.

Signed-off-by: Sascha Grunert <sgrunert@redhat.com>

Author: saschagrunert

go.mod

@@ -1,6 +1,6 @@
 module sigs.k8s.io/cri-tools
 
-go 1.26.4
+go 1.26.6
 
 require (
 	github.com/containerd/nri v0.12.1