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/envconfig.cpp

@@ -10,8 +10,7 @@
 #include <memory>
 #include <vector>
 
-namespace xrpl {
-namespace test {
+namespace xrpl::test {
 
 std::atomic<bool> envUseIPv4{false};
 
@@ -209,5 +208,4 @@ makeConfig(
 }
 
 }  // namespace jtx
-}  // namespace test
-}  // namespace xrpl
+}  // namespace xrpl::test