fix: use !isuppercase instead of lowercase in completion logic

we're not really interested in whether all chars are lowercase (which
is only true for letters); instead we want to determine
whether the user manually upper-cased any chars and treat that
as a signal that they care about the casing.

src/requests/completions.jl

@@ -30,7 +30,7 @@ using REPL
 Returns true if `s` starts with `prefix` or has a sufficiently high fuzzy score.
 """
 function is_completion_match(s::AbstractString, prefix::AbstractString, cutoff=3)
-    starter = if all(islowercase, prefix)
+    starter = if !any(isuppercase, prefix)
         startswith(lowercase(s), prefix)
     else
         startswith(s, prefix)