pmb.parse.kconfig: fix container check for kernels >= 6.1
Kernel 6.1 dropped CONFIG_MEMCG_SWAP: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=e55b9f96860f6c6026cff97966a740576285e07b
$ su pmos -c "pmbootstrap kconfig check"
[09:00:30] WARNING: linux-postmarketos-qcom-sdm845/config-postmarketos-qcom-sdm845.aarch64: CONFIG_MEMCG_SWAP should be set. See <https://wiki.postmarketos.org/wiki/kconfig#CONFIG_MEMCG_SWAP> for details.
[09:00:33] ERROR: kconfig check failed!