Rename test source files according to new pattern

test/Common/forcing_tests.jl

test/Common/grid_tests.jl

test/Common/math_tests.jl

test/Common/runtests.jl

test/Common/utils_tests.jl

test/Processes/HeatConduction/heat_conduction_tests.jl

test/Processes/HeatConduction/runtests.jl

test/Processes/HeatConduction/sfcc_tests.jl

test/Processes/Sources/runtests.jl

test/Processes/runtests.jl

test/Setup/runtests.jl

test/Setup/setup_tests.jl

test/Setup/stratigraphy_tests.jl

test/processes/runtests.jl

test/runtests.jl