[pyramid] Avoid shutting down the repository at exit if it's already shutting down

For install `cubicweb-ctl pyramid` command will explicitly call
`repo.shutdown()` so the atexit hook is redundant. Prevent the latter to be
executed when the repository is already shutting down (otherwise one gets an
assertion error).

--HG--
branch : 3.25

cubicweb/pyramid/__init__.py

@@ -226,7 +226,11 @@ def includeme(config):
     config.registry['cubicweb.registry'] = repo.vreg
 
     if cwconfig.mode != 'test':
-        atexit.register(repo.shutdown)
+        @atexit.register
+        def shutdown_repo():
+            if repo.shutting_down:
+                return
+            repo.shutdown
 
     if asbool(config.registry.settings.get('cubicweb.defaults', True)):
         config.include('cubicweb.pyramid.defaults')