gui: change example address from legacy (P2PKH) to bech32m (P2TR)

The dummy addresses have been computed with the following Python script
(executed under ./test/functional):

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from test_framework.segwit_addr import CHARSET, decode_segwit_address, encode_segwit_address
from test_framework.messages import sha256

output_key = sha256(b'bitcoin dummy taproot output key')
for network, hrp in [('mainnet', 'bc'), ('signet', 'tb'), ('testnet', 'tb'), ('regtest', 'bcrt')]:
    dummy_address = encode_segwit_address(hrp, 1, output_key)
    while decode_segwit_address(hrp, dummy_address) != (None, None):
        last_char = CHARSET[(CHARSET.index(dummy_address[-1]) + 1) % 32]
        dummy_address = dummy_address[:-1] + last_char
    print(f'{network:7} example address: {dummy_address}')
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Author: theStack

src/qt/guiutil.cpp

@@ -109,22 +109,21 @@ QFont fixedPitchFont(bool use_embedded_font)
     return QFontDatabase::systemFont(QFontDatabase::FixedFont);
 }
 
-// Just some dummy data to generate a convincing random-looking (but consistent) address
-static const uint8_t dummydata[] = {0xeb,0x15,0x23,0x1d,0xfc,0xeb,0x60,0x92,0x58,0x86,0xb6,0x7d,0x06,0x52,0x99,0x92,0x59,0x15,0xae,0xb1,0x72,0xc0,0x66,0x47};
-
-// Generate a dummy address with invalid CRC, starting with the network prefix.
+// Return a pre-generated dummy bech32m address (P2TR) with invalid checksum.
 static std::string DummyAddress(const CChainParams &params)
 {
-    std::vector<unsigned char> sourcedata = params.Base58Prefix(CChainParams::PUBKEY_ADDRESS);
-    sourcedata.insert(sourcedata.end(), dummydata, dummydata + sizeof(dummydata));
-    for(int i=0; i<256; ++i) { // Try every trailing byte
-        std::string s = EncodeBase58(sourcedata);
-        if (!IsValidDestinationString(s)) {
-            return s;
-        }
-        sourcedata[sourcedata.size()-1] += 1;
-    }
-    return "";
+    switch (params.GetChainType()) {
+    case ChainType::MAIN:
+        return "bc1p35yvjel7srp783ztf8v6jdra7dhfzk5jaun8xz2qp6ws7z80n4tq2jku9f";
+        break;
+    case ChainType::SIGNET:
+    case ChainType::TESTNET:
+        return "tb1p35yvjel7srp783ztf8v6jdra7dhfzk5jaun8xz2qp6ws7z80n4tqa6qnlg";
+        break;
+    case ChainType::REGTEST:
+        return "bcrt1p35yvjel7srp783ztf8v6jdra7dhfzk5jaun8xz2qp6ws7z80n4tqsr2427";
+    } // no default case, so the compiler can warn about missing cases
+    assert(false);
 }
 
 void setupAddressWidget(QValidatedLineEdit *widget, QWidget *parent)