(#15471) Fix setting mode of last_run_summary

The writlock function didn't work with setting the mode on the
last_run_summary file. This backports some of the work in commit
7d8fd144949f21eff924602c2a6b7f130f1c0b69. Specifically, the changes
from using writelock to replace_file for saving the summary file. This
builds on top of the backport of getting replace_file to work on
windows.