build-unit-test-docker: update to clang-15
build-unit-test-docker: update to clang-15

Signed-off-by: Patrick Williams <cbb7353e6d953ef360baf960c122346276c6e320@stwcx.xyz>
Change-Id: Id5532b96a7067ea831c3fcd67418a85314a3e840

openbmc/openbmc-build-scripts,openbmc/openbmc-build-scripts