ICU-23152 Another typename

icu4c/source/common/unicode/bytestream.h

diff --git a/icu4c/source/common/unicode/bytestream.h b/icu4c/source/common/unicode/bytestream.h
index b2cd9b8..224899b 100644
--- a/icu4c/source/common/unicode/bytestream.h
+++ b/icu4c/source/common/unicode/bytestream.h
@@ -289,7 +289,7 @@ using value_type_or_char_t = typename value_type_or_char<StringClass>::type;
  */
 template<typename StringClass>
 class StringByteSink : public ByteSink {
-  using Unit = prv::value_type_or_char_t<StringClass>;
+  using Unit = typename prv::value_type_or_char_t<StringClass>;
  public:
   /**
    * Constructs a ByteSink that will append bytes to the dest string.