Re-enable `test_loading_kokkos`

[s-sajid-ali]

test_loading_kokkos.cc was temporarily disabled in #148 as the errors were unrelated to the PR. Understand the root cause of the failure and fix it.

Last CI failure has:

[126/389] Building CXX object src/synergia/utils/tests/CMakeFiles/test_loading_kokkos.dir/test_loading_kokkos.cc.o
FAILED: src/synergia/utils/tests/CMakeFiles/test_loading_kokkos.dir/test_loading_kokkos.cc.o 
/usr/bin/clang++-15 -DBUILD_FD_SPACE_CHARGE_SOLVER -DGSV_AVX -DMPICH_SKIP_MPICXX -DNO_PADDING -DOMPI_SKIP_MPICXX -DSYNERGIA_ENABLE_OPENMP=1 -DSYNERGIA_HAVE_OPENPMD -DUSE_PARALLEL_HDF5 -D_MPICC_H -I/__w/synergia2/synergia2/src -I/__w/synergia2/synergia2/src/synergia/utils -I/home/runner/work/synergia2/synergia2/build/src/synergia/utils/kokkos -I/home/runner/work/synergia2/synergia2/build/src/synergia/utils/kokkos/core/src -I/home/runner/work/synergia2/synergia2/build/src/synergia/utils/kokkos/core/src/desul -I/__w/synergia2/synergia2/src/synergia/utils/kokkos/tpls/desul/include -I/__w/synergia2/synergia2/src/synergia/utils/kokkos/core/src -stdlib=libc++ -Wno-#pragma-messages -Wno-potentially-evaluated-expression -Wno-register -O2 -g -DNDEBUG -std=c++17 -MD -MT src/synergia/utils/tests/CMakeFiles/test_loading_kokkos.dir/test_loading_kokkos.cc.o -MF src/synergia/utils/tests/CMakeFiles/test_loading_kokkos.dir/test_loading_kokkos.cc.o.d -o src/synergia/utils/tests/CMakeFiles/test_loading_kokkos.dir/test_loading_kokkos.cc.o -c /__w/synergia2/synergia2/src/synergia/utils/tests/test_loading_kokkos.cc
In file included from /__w/synergia2/synergia2/src/synergia/utils/tests/test_loading_kokkos.cc:4:
In file included from /__w/synergia2/synergia2/src/synergia/utils/kokkos/core/src/Kokkos_Core.hpp:45:
In file included from /home/runner/work/synergia2/synergia2/build/src/synergia/utils/kokkos/KokkosCore_Config_DeclareBackend.hpp:22:
In file included from /__w/synergia2/synergia2/src/synergia/utils/kokkos/core/src/decl/Kokkos_Declare_OPENMP.hpp:21:
In file included from /__w/synergia2/synergia2/src/synergia/utils/kokkos/core/src/Kokkos_OpenMP.hpp:188:
/__w/synergia2/synergia2/src/synergia/utils/kokkos/core/src/OpenMP/Kokkos_OpenMP_Instance.hpp:23:2: error: "You enabled Kokkos OpenMP support without enabling OpenMP in the compiler!"
#error \
 ^
1 error generated.

https://github.com/fnalacceleratormodeling/synergia2/actions/runs/4491583120/jobs/7900242299?pr=148

CMake Output from the same log has:

-- Using vendored copy of kokkos
-- Setting default Kokkos CXX standard to 17
-- The project name is: Kokkos
-- Using internal gtest for testing
-- Configured git information in /home/runner/work/synergia2/synergia2/build/generated/Kokkos_Version_Info.cpp
-- Using -std=c++17 for C++17 standard as feature
-- Built-in Execution Spaces:
--     Device Parallel: NoTypeDefined
--     Host Parallel: Kokkos::OpenMP
--       Host Serial: NONE
-- 
-- Architectures:
-- Found TPLLIBDL: /usr/include  
-- Found OpenMP_C: -fopenmp=libomp (found version "5.0") 
-- Found OpenMP_CXX: -fopenmp=libomp (found version "5.0") 
-- Using internal desul_atomics copy
-- Kokkos Devices: OPENMP, Kokkos Backends: OPENMP