increase niter_part in convergence test

tests/test_convergence.py

@@ -49,6 +49,7 @@ def convergence_test(
     opt.n *= 2
     opt.niter_todo *= 2
     opt.niter_stat *= 2
+    opt.niter_part *= 2
     opt.ncpu *= 2
     opt.simname = 'N{0:0>3x}'.format(opt.n)
     c1 = code_launch_routine(
@@ -61,6 +62,7 @@ def convergence_test(
     opt.n *= 2
     opt.niter_todo *= 2
     opt.niter_stat *= 2
+    opt.niter_part *= 2
     opt.ncpu *= 2
     opt.simname = 'N{0:0>3x}'.format(opt.n)
     c2 = code_launch_routine(