Redis [BUG] Blocking reads don't work on Redis Cluster replica nodes

Describe the bug

Blocking reads on Redis Cluster replica nodes (in readonly mode) always get redirected to a master node.

To reproduce

Connect to a replica node, go into a readonly mode, do a blocking read, e.g.:

127.0.0.1:6381> CONNECT 127.0.0.1 6385
127.0.0.1:6385> READONLY
OK
127.0.0.1:6385> XREAD STREAMS k 0
(nil)
127.0.0.1:6385> XREAD BLOCK 100 STREAMS k 0
-> Redirected to slot [7629] located at 127.0.0.1:6381
(nil)
127.0.0.1:6381> 

Expected behavior

According to documentation of READONLY:

When the connection is in readonly mode, the cluster will send a redirection to the client only if the operation involves keys not served by the replica's master node.

blocking reads should not get redirected to a master node.

Additional information

IIUC the clusterRedirectBlockedClientIfNeeded does not handle the case when the blocking read is on a replica node: https://github.com/redis/redis/blob/3945a321779a0be52e556aa11babb3fe15883a78/src/cluster.c#L5856-L5862

Comment From: oranagra

@o948 thanks for reporting, please have a look at the fix in #7881 and let me know what you think.

Comment From: o948

Thanks for a quick fix, looks good to me. Do you know whether this fix is important enough to go to the next minor 5.0 release?

Comment From: oranagra

it's relatively safe, so it can get there, but i'm not sure if / when we'll make another 5.0 release. we are likely to do that only if there's some critical issue that's found. i'll mark the PR for followup.