Add EXT4_FEATURE_INCOMPAT_CSUM_SEED to EXT2_DRIVER_IGNORED_INCOMPAT

[markpeek]

After installing alpine-standard-3.20.1-x86_64.iso into a bhyve VM, grub did not recognize the filesystem and would not boot. This was caused by the filesystem using the metadata_csum_seed feature that was not supported by this version of grub.

This is from the installed alpine (note the "metadata_csum_seed"):

# dumpe2fs /dev/vda3 | grep "Filesystem feature"
dumpe2fs 1.47.0 (5-Feb-2023)
Filesystem features:      has_journal ext_attr resize_inode dir_index orphan_file filetype needs_recovery extent 64bit flex_bg metadata_csum_seed sparse_super large_file huge_file dir_nlink extra_isize metadata_csum orphan_present

The upstream code has this change here:
https://git.savannah.gnu.org/cgit/grub.git/tree/grub-core/fs/ext2.c#n118

Note: it might make sense to add the other ignored FEATURES (*_MMP and *LARGEDIR) as well.

[grehan-freebsd]

Just to confirm: that was the only change required for Alpine to boot ?