correct typo in FM tutorial

Author: kilianFatras

examples/2D_tutorials/Flow_matching_tutorial.ipynb

@@ -511,7 +511,7 @@
     "    x0, x1 = ot_sampler.sample_plan(x0, x1)\n",
     "\n",
     "    t = torch.rand(x0.shape[0]).type_as(x0)\n",
-    "    xt = sample_xt(x0, x1, t, sigma=0.01)\n",
+    "    xt = sample_conditional_pt(x0, x1, t, sigma=0.01)\n",
     "    ut = compute_conditional_vector_field(x0, x1)\n",
     "\n",
     "    vt = model(torch.cat([xt, t[:, None]], dim=-1))\n",