Add GLNX_FILE_REPLACE_INCREASING_MTIME

This make replaced files have a strictly increasing st_mtime. The main usecase I have for this is to ensure the summary file mtime increases because the flatpak tests are failing due to the python httpd used in the tests rely on st_mtime for the http If-Modified-Since header.

For the tests this breaks all the time since we're just doing a lot of summary updates. However, I can see this accidentally happening in the wild too, so i think its proper to always ensure the new summary is "newer", even though it means it will be timestamped slightly in the future. In practice this will not happen regularly, and the times it does happen we really do need it.