Fix flaky redis-cli reverse search no-result test (#15119)

## Problem

The `redis-cli` reverse-search test for the no-result case can be flaky
in slower CI environments.

`read_cli` may return too early when CLI output is fragmented or
delayed. It currently gives up after only 5 consecutive empty reads,
with a 10ms delay between reads, which can make the test assert before
the expected `(empty array)` output is printed.

## Changes

Increase the `read_cli` consecutive empty-read threshold from `5` to
`100`.

This keeps the existing read behavior unchanged when data is available,
but allows the helper to wait longer for delayed/fragmented CLI output
before giving up.

---------

Co-authored-by: debing.sun <debing.sun@redis.com>

tests/integration/redis-cli.tcl

@@ -42,7 +42,7 @@ start_server {tags {"cli"}} {
 
         # We may have a short read, try to read some more.
         set empty_reads 0
-        while {$empty_reads < 5} {
+        while {$empty_reads < 100} {
             set buf [read $fd]
             if {[string length $buf] == 0} {
                 after 10