Update the configuration for Travis CI and AppVeyor CI Update the Travis CI matrix: * Run ASan and UBSan unconditionally on FreeBSD and Linux, and not at all on Mac. * Remove the `CI_NO_TEST=1` runs from the environment column. Update the AppVeyor CI matrix: * Replace `CI_NO_TEST=1` with `CI_CMAKE_VARS=-DPNG_TESTS=0` when testing Visual Studio on ARM64. Also apply minor stylistic changes.