Add folkertdev to crate-maintainers

[joshtriplett]

Folkert has been doing great work in the ecosystem on
zlib-rs, flate2, libz-sys, and libz-ng-sys.

[github-actions]

Dry-run check results

[WARN  rust_team::sync] sync-team is running in dry mode, no changes will be applied.
[INFO  rust_team::sync] synchronizing crates-io
[INFO  rust_team::sync] synchronizing github
[INFO  rust_team::sync] 💻 Team Diffs:
    📝 Editing team 'rust-lang/crate-maintainers':
      Adding member 'folkertdev' with member role

[joshtriplett]

This was still being discussed, and waiting on approval. (AIUI, we normally wait for confirmation from another team member before merging?)

[jieyouxu]

Oh sorry, I thought this was already approved! My bad

EDIT: reverted this in #2480 since it's still being discussed, can you please re-open a PR re-adding folkertdev? Sorry for the inconvenience