valgrind_ctime_test: Add schnorrsig_sign

Summary:
This is a partial backport of secp256k1 [[bitcoin-core/secp256k1#558 | PR558]] : bitcoin-core/secp256k1@f431b3f

Depends on D7650

Test Plan:
  ninja check-secp256k1

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D7651

src/valgrind_ctime_test.c

@@ -25,6 +25,10 @@
 # include "include/secp256k1_extrakeys.h"
 #endif
 
+#if ENABLE_MODULE_SCHNORRSIG
+#include "include/secp256k1_schnorrsig.h"
+#endif
+
 int main(void) {
     secp256k1_context* ctx;
     secp256k1_ecdsa_signature signature;
@@ -151,6 +155,16 @@ int main(void) {
     CHECK(ret == 1);
 #endif
 
+#if ENABLE_MODULE_SCHNORRSIG
+    VALGRIND_MAKE_MEM_UNDEFINED(key, 32);
+    ret = secp256k1_keypair_create(ctx, &keypair, key);
+    VALGRIND_MAKE_MEM_DEFINED(&ret, sizeof(ret));
+    CHECK(ret == 1);
+    ret = secp256k1_schnorrsig_sign(ctx, sig, msg, &keypair, NULL, NULL);
+    VALGRIND_MAKE_MEM_DEFINED(&ret, sizeof(ret));
+    CHECK(ret == 1);
+#endif
+
     secp256k1_context_destroy(ctx);
     return 0;
 }