C23 compatibility: don't use false as NULL (#307)

Co-authored-by: Philip Odom <philip@firia.com>
diff --git a/src/qcbor_decode.c b/src/qcbor_decode.c
index 0f4d5c0..05e9c87 100644
--- a/src/qcbor_decode.c
+++ b/src/qcbor_decode.c
@@ -4238,7 +4238,7 @@
     * level is reached.  It may do nothing, or ascend all the way to
     * the top level.
     */
-   uErr = QCBORDecode_Private_NestLevelAscender(pMe, NULL, false);
+   uErr = QCBORDecode_Private_NestLevelAscender(pMe, NULL, NULL);
    if(uErr != QCBOR_SUCCESS) {
       goto Done;
    }