unexpected relkind: 73 ERROR with partition table index

create user u1 superuser;
create user u2 nosuperuser login;
\c postgres u1

create table public.part(c1 int, c2 int) partition by range(c1);
create table public.part_p1 partition of public.part for values from (minvalue) to (0);
create table public.part_p2 partition of public.part for values from (0) to (maxvalue);
create index part_idx on public.part(c1);

create table public.nopart (c1 int, c2 int);
create index nopart_idx on public.nopart(c1);

--switch to nonsuperuser
\c postgres u2

postgres=> --rename the index owned by another user --non partition table
postgres=> ALTER INDEX nopart_idx RENAME TO nopart_idx_renamed;
ERROR:  must be owner of index nopart_idx
postgres=>
postgres=> --rename the index owned by another user --partition table
postgres=> ALTER INDEX part_idx RENAME TO part_idx_renamed;
ERROR:  unexpected relkind: 73