chore: Enable clang-tidy modernize checks (#6975)

Co-authored-by: Bart <11445373+bthomee@users.noreply.github.com>
Co-authored-by: Bart <bthomee@users.noreply.github.com>

src/test/jtx/impl/Account.cpp

@@ -19,9 +19,7 @@
 #include <unordered_map>
 #include <utility>
 
-namespace xrpl {
-namespace test {
-namespace jtx {
+namespace xrpl::test::jtx {
 
 std::unordered_map<std::pair<std::string, KeyType>, Account, beast::uhash<>> Account::cache_;
 
@@ -95,6 +93,4 @@ Account::operator[](std::string const& s) const
     return IOU(*this, currency);
 }
 
-}  // namespace jtx
-}  // namespace test
-}  // namespace xrpl
+}  // namespace xrpl::test::jtx