upgrade kubectl to 1.26.x

Due to https://gitlab.com/gitlab-org/build/CNG/-/issues/1861+ ( see https://gitlab.com/gitlab-org/build/CNG/-/issues/1861#note_1806272808 ) kubectl needs to be bumped to a more recent version.

Given that we've bumped minimum supported of kubernetes to 1.25 it should be safe to bump kubectl to 1.26 given Kubernetes compatibility within one minor release.