[lldb] Fix -Wctad-maybe-unsupported in PathMappingList.cpp (NFC)

/home/jiefu/llvm-project/lldb/source/Target/PathMappingList.cpp:51:5: error: 'scoped_lock' may not intend to support class template argument deduction [-Werror,-Wctad-maybe-unsupported]
    std::scoped_lock locks(m_mutex, rhs.m_mutex);
    ^
/usr/lib/gcc/x86_64-linux-gnu/12/../../../../include/c++/12/mutex:692:11: note: add a deduction guide to suppress this warning
    class scoped_lock
          ^
/home/jiefu/llvm-project/lldb/source/Target/PathMappingList.cpp:72:3: error: 'scoped_lock' may not intend to support class template argument deduction [-Werror,-Wctad-maybe-unsupported]
  std::scoped_lock locks(m_mutex, rhs.m_mutex);
  ^
/usr/lib/gcc/x86_64-linux-gnu/12/../../../../include/c++/12/mutex:692:11: note: add a deduction guide to suppress this warning
    class scoped_lock
          ^
2 errors generated.