Merge bitcoin#31248: test: Rework wallet_migration.py to use previous releases

55347a5 test: Rework migratewallet to use previous release (v28.0) (Ava Chow)
f42ec0f wallet: Check specified wallet exists before migration (Ava Chow)

Pull request description:

  This PR reworks wallet_migration.py to use previous releases to produce legacy wallets for testing so that the test will continue to work once legacy wallets are removed.

  Split from bitcoin#28710

ACKs for top commit:
  maflcko:
    re-ACK 55347a5 🥊
  rkrux:
    re-ACK 55347a5

Tree-SHA512: f90a2f475febc73d29e8ad3cb20d134c368a40a3b5934c3e4aaa77ae704af6314d4dd2e85c261142bd60a201902ac4ba00b8e2443d3cef7c8cc45d23281fa831

Author: ryanofsky

src/wallet/wallet.cpp

@@ -4407,6 +4407,9 @@ util::Result<MigrationResult> MigrateLegacyToDescriptor(const std::string& walle
         if (!wallet_path) {
             return util::Error{util::ErrorString(wallet_path)};
         }
+        if (!fs::exists(*wallet_path)) {
+            return util::Error{_("Error: Wallet does not exist")};
+        }
         if (!IsBDBFile(BDBDataFile(*wallet_path))) {
             return util::Error{_("Error: This wallet is already a descriptor wallet")};
         }