Fix 'Client output buffer hard limit is enforced' test causing infinite loop (#13934)

This PR fixes an issue in the CI test for client-output-buffer-limit,
which was causing an infinite loop when running on macOS 15.4.

### Problem

This test start two clients, R and R1:
```c
R1 subscribe foo
R publish foo bar
```

When R executes `PUBLISH foo bar`, the server first stores the message
`bar` in R1‘s buf. Only when the space in buf is insufficient does it
call `_addReplyProtoToList`.
Inside this function, `closeClientOnOutputBufferLimitReached` is invoked
to check whether the client’s R1 output buffer has reached its
configured limit.
On macOS 15.4, because the server writes to the client at a high speed,
R1’s buf never gets full. As a result,
`closeClientOnOutputBufferLimitReached` in the test is never triggered,
causing the test to never exit and fall into an infinite loop.

---------

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

tests/unit/obuf-limits.tcl

@@ -37,7 +37,9 @@ start_server {tags {"obuf-limits external:skip logreqres:skip"}} {
 
         set omem 0
         while 1 {
-            r publish foo bar
+            # The larger content size ensures that client.buf gets filled more quickly,
+            # allowing us to correctly observe the gradual increase of `omem`
+            r publish foo [string repeat bar 50]
             set clients [split [r client list] "\r\n"]
             set c [split [lindex $clients 1] " "]
             if {![regexp {omem=([0-9]+)} $c - omem]} break