Merge pull request #1511 from UXARRAY/rajeeja/fix_healpix_notebook

 Fix broken healpix notebook

Author: rajeeja

docs/user-guide/healpix.ipynb

@@ -147,13 +147,22 @@
    "source": [
     "(\n",
     "    ux.Grid.from_healpix(zoom=2).plot(\n",
-    "        periodic_elements=\"split\", projection=ccrs.Orthographic(), title=\"zoom=2\"\n",
+    "        periodic_elements=\"split\",\n",
+    "        projection=ccrs.Orthographic(),\n",
+    "        title=\"zoom=2\",\n",
+    "        backend=\"matplotlib\",\n",
     "    )\n",
     "    + ux.Grid.from_healpix(zoom=3).plot(\n",
-    "        periodic_elements=\"split\", projection=ccrs.Orthographic(), title=\"zoom=3\"\n",
+    "        periodic_elements=\"split\",\n",
+    "        projection=ccrs.Orthographic(),\n",
+    "        title=\"zoom=3\",\n",
+    "        backend=\"matplotlib\",\n",
     "    )\n",
     "    + ux.Grid.from_healpix(zoom=4).plot(\n",
-    "        periodic_elements=\"split\", projection=ccrs.Orthographic(), title=\"zoom=4\"\n",
+    "        periodic_elements=\"split\",\n",
+    "        projection=ccrs.Orthographic(),\n",
+    "        title=\"zoom=4\",\n",
+    "        backend=\"matplotlib\",\n",
     "    )\n",
     ").cols(1)"
    ]