Fix -Wmissing-template-arg-list-after-template-kw issued by Clang 19

[dummyunit]

This warning is treated as error by default:
https://releases.llvm.org/19.1.0/tools/clang/docs/DiagnosticsReference.html#wmissing-template-arg-list-after-template-kw
So build breaks for all library consumers even when -Werror, -Wall, etc. are not used.

STR:

$ CXX=clang++-19 CC=clang-19 cmake -B build -DATOMIC_QUEUE_BUILD_TESTS=yes &> /dev/null
$ cmake --build build
[  0%] Built target atomic_queue
[ 50%] Building CXX object src/CMakeFiles/atomic_queue_tests.dir/tests.cc.o
In file included from /tmp/atomic_queue/src/tests.cc:8:
/tmp/atomic_queue/include/atomic_queue/atomic_queue.h:407:31: error: a template argument list is expected after a name prefixed by the template keyword [-Wmissing-template-arg-list-after-template-kw]
  407 |         return Base::template do_pop_any(states_[index], elements_[index]);
      |                               ^
/tmp/atomic_queue/include/atomic_queue/atomic_queue.h:413:24: error: a template argument list is expected after a name prefixed by the template keyword [-Wmissing-template-arg-list-after-template-kw]                                                                                   
  413 |         Base::template do_push_any(std::forward<U>(element), states_[index], elements_[index]);
      |                        ^
/tmp/atomic_queue/include/atomic_queue/atomic_queue.h:538:31: error: a template argument list is expected after a name prefixed by the template keyword [-Wmissing-template-arg-list-after-template-kw]                                                                                   
  538 |         return Base::template do_pop_any(states_[index], elements_[index]);
      |                               ^
/tmp/atomic_queue/include/atomic_queue/atomic_queue.h:544:24: error: a template argument list is expected after a name prefixed by the template keyword [-Wmissing-template-arg-list-after-template-kw]                                                                                   
  544 |         Base::template do_push_any(std::forward<U>(element), states_[index], elements_[index]);
      |                        ^
4 errors generated.

[max0x7ba]

Thank you for your contribution.

For some reason, this piece of code came to my mind yesterday, out of the blue, and a question arose why template was there.