gh-116146: Avoid empty braces in _testembed.c

[encukou]

• Issue: Expose a C-API function to allow custom importers to create a module using an init function #116146

[encukou]

This broke a buildbot: https://buildbot.python.org/#/builders/1079/builds/7471

[itamaro]

Thanks for the quick fix @encukou !