util/DynamicFifoBuffer: use `T` instead of `std::byte`

Mistake added by commit b528b467649754

src/util/DynamicFifoBuffer.hxx

@@ -83,7 +83,7 @@ public:
 	/**
 	 * Append data to the buffer, growing it as needed.
 	 */
-	void Append(std::span<const std::byte> src) noexcept {
+	void Append(std::span<const T> src) noexcept {
 		std::copy(src.begin(), src.end(), Write(src.size()));
 		Append(src.size());
 	}