Remove empty line from tests/variable/variable.cpp to satisfy clang format.
Remove empty line from tests/variable/variable.cpp to satisfy clang format.

hsorby/libcellml,nickerso/libcellml,hsorby/libcellml,cellml/libcellml,cellml/libcellml,nickerso/libcellml,nickerso/libcellml,MichaelClerx/libcellml,cellml/libcellml,MichaelClerx/libcellml,hsorby/libcellml,MichaelClerx/libcellml,hsorby/libcellml,nickerso/libcellml,cellml/libcellml