fuzz-varlink-idl: use ASSERT_OK() and friends

Replace assert_se() with the typed ASSERT_* macros, so that a failing
assertion logs the values involved.

src/fuzz/fuzz-varlink-idl.c

@@ -5,6 +5,7 @@
 #include "alloc-util.h"
 #include "fuzz.h"
 #include "log.h"
+#include "tests.h"
 #include "varlink-idl-util.h"
 
 int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
@@ -17,7 +18,7 @@ int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
 
         fuzz_setup_logging();
 
-        assert_se(str = memdup_suffix0(data, size));
+        str = ASSERT_NOT_NULL(memdup_suffix0(data, size));
 
         r = sd_varlink_idl_parse(str, /* reterr_line= */ NULL, /* reterr_column= */ NULL, &vi);
         if (r < 0) {
@@ -25,7 +26,7 @@ int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
                 return 0;
         }
 
-        assert_se(sd_varlink_idl_format(vi, &dump) >= 0);
+        ASSERT_OK(sd_varlink_idl_format(vi, &dump));
         (void) varlink_idl_consistent(vi, LOG_DEBUG);
 
         return 0;