refactor: Pass script verify flags as uint32_t

They are cast to unsigned anyway when calling VerifyScript,
bitcoinconsensus_verify_script*, or CountWitnessSigOps.

src/bench/verify_script.cpp

@@ -21,7 +21,7 @@ static void VerifyScriptBench(benchmark::Bench& bench)
     const ECCVerifyHandle verify_handle;
     ECC_Start();
 
-    const int flags = SCRIPT_VERIFY_WITNESS | SCRIPT_VERIFY_P2SH;
+    const uint32_t flags{SCRIPT_VERIFY_WITNESS | SCRIPT_VERIFY_P2SH};
     const int witnessversion = 0;
 
     // Key pair.