How can I stop Linux from changing Windows's clock?

Run this command to make Linux use local time. This will resolve the issue.

timedatectl set-local-rtc 1 --adjust-system-clock

On the Windows computer, open the Registry Editor (Run… regedit.exe) and navigate to HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\TimeZoneInformation. Create a DWORD named RealTimeIsUniversal, and set its value to 1.

– Adapted from Ricardo Bohner's answer

Linux and other *nixes assume that your hardware clock is set to UTC, and simply corrects the clock that is displayed to a user. Windows, however, sets the hardware clock to the local time, correcting it to UTC when it is needed (i.e. networking, etc). By setting this in the registry, you are telling Windows that the hardware clock is UTC, and should be corrected to local time when shown to the user.