test: guard coupler_transfer behind PCMS_ENABLE_PETSC

test_coupler_transfer.cpp pulls in the PETSc-dependent transfer headers,
so the target cannot compile when PETSc is disabled. Guard it like the
other transfer tests (PCMS_ENABLE_PETSC AND PCMS_ENABLE_MESHFIELDS).

Author: jacobmerson

test/CMakeLists.txt

@@ -214,6 +214,7 @@ if(PCMS_ENABLE_OMEGA_H)
       ${d3d1p}
       ignored)
   endif()
+  if(PCMS_ENABLE_PETSC AND PCMS_ENABLE_MESHFIELDS)
   add_executable(coupler_transfer test_coupler_transfer.cpp)
   target_link_libraries(coupler_transfer PUBLIC pcms::core test_support)
   if(HOST_NPROC GREATER_EQUAL 4)
@@ -253,6 +254,7 @@ if(PCMS_ENABLE_OMEGA_H)
       ${d3d1p}
       ignored)
   endif()
+  endif()
   if(HOST_NPROC GREATER_EQUAL 26)
     tri_mpi_test(
       TESTNAME