Increase the size of boot partition.

initramfs is now updated atomically which requires extra free space to have both the old and new version at the same time during the update (https://gitlab.com/postmarketOS/pmaports/-/commit/ed3eeeeebb1e4ea7b93c48280bd6a5bd94b44865). The increase is probably a bit too much, but as you need to reflash to increase the size of the partition, it's probably worth it.