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/flags.cpp

@@ -9,9 +9,7 @@
 
 #include <cstdint>
 
-namespace xrpl {
-namespace test {
-namespace jtx {
+namespace xrpl::test::jtx {
 
 Json::Value
 fset(Account const& account, std::uint32_t on, std::uint32_t off)
@@ -62,6 +60,4 @@ nflags::operator()(Env& env) const
     }
 }
 
-}  // namespace jtx
-}  // namespace test
-}  // namespace xrpl
+}  // namespace xrpl::test::jtx