/usr/share/dbus-1/services/org.gnome.Calendar.service is in gnome-calendar 3.22.4-2.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 | [D-BUS Service]
Name=org.gnome.Calendar
Exec=/usr/bin/gnome-calendar --gapplication-service
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