wallet, logging: Switch LogInfo to LogError in AddWalletDescriptor

Seems like all of these cases are treated as errors, so it makes sense to use
the corresponding log level.

Change suggested by hodlinator in bitcoin#30343 (comment)

src/wallet/wallet.cpp

@@ -3923,13 +3923,13 @@ ScriptPubKeyMan* CWallet::AddWalletDescriptor(WalletDescriptor& desc, const Flat
     AssertLockHeld(cs_wallet);
 
     if (!IsWalletFlagSet(WALLET_FLAG_DESCRIPTORS)) {
-        LogInfo(m_log, "Cannot add WalletDescriptor to a non-descriptor wallet\n");
+        LogError(m_log, "Cannot add WalletDescriptor to a non-descriptor wallet\n");
         return nullptr;
     }
 
     auto spk_man = GetDescriptorScriptPubKeyMan(desc);
     if (spk_man) {
-        LogInfo(m_log, "Update existing descriptor: %s\n", desc.descriptor->ToString());
+        LogError(m_log, "Update existing descriptor: %s\n", desc.descriptor->ToString());
         spk_man->UpdateWalletDescriptor(desc);
     } else {
         auto new_spk_man = std::unique_ptr<DescriptorScriptPubKeyMan>(new DescriptorScriptPubKeyMan(*this, desc, m_keypool_size));
@@ -3948,7 +3948,7 @@ ScriptPubKeyMan* CWallet::AddWalletDescriptor(WalletDescriptor& desc, const Flat
 
     // Top up key pool, the manager will generate new scriptPubKeys internally
     if (!spk_man->TopUp()) {
-        LogInfo(m_log, "Could not top up scriptPubKeys\n");
+        LogError(m_log, "Could not top up scriptPubKeys\n");
         return nullptr;
     }
 
@@ -3957,7 +3957,7 @@ ScriptPubKeyMan* CWallet::AddWalletDescriptor(WalletDescriptor& desc, const Flat
     if (!desc.descriptor->IsRange()) {
         auto script_pub_keys = spk_man->GetScriptPubKeys();
         if (script_pub_keys.empty()) {
-            LogInfo(m_log, "Could not generate scriptPubKeys (cache is empty)\n");
+            LogError(m_log, "Could not generate scriptPubKeys (cache is empty)\n");
             return nullptr;
         }