Fix gcc conversion warning in BitStreamReader

Author: mikir

compiler/extensions/cpp/runtime/src/zserio/BitStreamWriter.cpp

@@ -555,7 +555,7 @@ void BitStreamWriter::writeUnsignedBits(uint32_t data, uint8_t numBits)
     {
         // first part
         const uint8_t shiftNum = restNumBits - bitsFree;
-        const uint8_t maskedByte = m_buffer[byteIndex] & ~(0xFFU >> bitsUsed);
+        const uint8_t maskedByte = m_buffer[byteIndex] & static_cast<uint8_t>(~(0xFFU >> bitsUsed));
         m_buffer[byteIndex++] = maskedByte | static_cast<uint8_t>(data >> shiftNum);
         restNumBits -= bitsFree;