Fix long commented line in pgi notebook

Author: santisoler

notebooks/12-pgi-inversion/plot_inv_1_joint_pf_pgi_full_info_tutorial.ipynb

@@ -519,7 +519,8 @@
     "    covariance_type=\"diag\",  # diagonal covariances\n",
     ")\n",
     "# required: initialization with fit\n",
-    "# fake random samples, size of the mesh, number of physical properties: 2 (density and mag.susc)\n",
+    "# fake random samples, size of the mesh,\n",
+    "# number of physical properties: 2 (density and mag.susc)\n",
     "rng = np.random.default_rng(seed=518936)\n",
     "gmmref.fit(rng.normal(size=(nactv, 2)))\n",
     "# set parameters manually\n",