gnome-todo-40.1 fails to build in 1-core VM

Building gnome-todo-40.1 for openSUSE-Tumbleweed with

osc co openSUSE:Factory/gnome-todo && cd $_
osc build --noservice --vm-type=kvm --clean -j1 standard

fails with

 cc ... -o src/plugins/libplugins.a.p/all-tasks-panel_all-tasks-panel-plugin.c.o -c ../src/plugins/all-tasks-panel/all-tasks-panel-plugin.c
 In file included from ../src/plugins/all-tasks-panel/all-tasks-panel-plugin.c:24: 
 ../src/gnome-todo.h:24:10: fatal error: gtd-enum-types.h: No such file or directory
    24 | #include "gtd-enum-types.h"
       |          ^~~~~~~~~~~~~~~~~~
 compilation terminated.
 ninja: build stopped: subcommand failed.

Our build instructions can be seen at https://code.opensuse.org/package/gnome-todo/blob/master/f/gnome-todo.spec#_76

This bug was found while working on reproducible builds for openSUSE.