Add ext4 to the syschecks FS check

We semi-support ext4 but in the syscheck we will now check for both
ext2 and ext4, as currently ext4 is always detected as ext2, but
in the future if ext4 is returned we should also treat this as ext4.

Issue redpanda-data#13469.

Author: travisdowns

src/v/syschecks/syschecks.cc

@@ -51,10 +51,12 @@ ss::future<> disk(const ss::sstring& path) {
     return ss::check_direct_io_support(path).then([path] {
         return ss::file_system_at(path).then([path](auto fs) {
             checklog.info0("Detected file system type is {}", to_string(fs));
-            // all of ext2, 3 and 4 are detected as ext2, so we just assume an
-            // ext2 detection means ext4 for now, see:
+            // Currently, all of ext2, 3 and 4 are detected as ext2, so we just
+            // assume an ext2 detection means ext4 for now, see:
             // https://github.com/redpanda-data/redpanda/issues/13469
-            if (fs == ss::fs_type::ext2) {
+            // We also still check for ext4, since if that is returned it means
+            // that seastar has been fixed to be able to detect ext4.
+            if (fs == ss::fs_type::ext2 || fs == ss::fs_type::ext4) {
                 checklog.warn(
                   "Path: `{}' is on ext4, not XFS. This will probably work, "
                   "but Redpanda is only tested on XFS and XFS is recommended "