Clarifying ispunct behavior difference between Julia and C in documentation (#56727)

Fixes #56680. This PR updates the documentation for the ispunct function
in Julia to explicitly note its differing behavior from the similarly
named function in C.

---------

Co-authored-by: Lilith Orion Hafner <[email protected]>

Author: Priynsh

base/strings/unicode.jl

@@ -534,11 +534,17 @@ iscntrl(c::AbstractChar) = c <= '\x1f' || '\x7f' <= c <= '\u9f'
 Tests whether a character belongs to the Unicode general category Punctuation, i.e. a
 character whose category code begins with 'P'.
 
+!!! note
+    This behavior is different from the `ispunct` function in C.
+
 # Examples
 ```jldoctest
 julia> ispunct('α')
 false
 
+julia> ispunct('=')
+false
+
 julia> ispunct('/')
 true