Fix backend tutorial warning

Author: dcherian

advanced/backends/1.Backend_without_Lazy_Loading.ipynb

@@ -17,20 +17,20 @@
     "## BackendEntrypoint\n",
     "Implement a subclass of `BackendEntrypoint` that expose a method `open_dataset`:\n",
     "\n",
-    "   ```python\n",
-    "    from xarray.backends import BackendEntrypoint\n",
+    "```python\n",
+    "from xarray.backends import BackendEntrypoint\n",
+    "\n",
+    "class MyBackendEntrypoint(BackendEntrypoint):\n",
+    "    def open_dataset(\n",
+    "        self,\n",
+    "        filename_or_obj,\n",
+    "        *,\n",
+    "        drop_variables=None,\n",
+    "    ):\n",
     "\n",
-    "    class MyBackendEntrypoint(BackendEntrypoint):\n",
-    "        def open_dataset(\n",
-    "            self,\n",
-    "            filename_or_obj,\n",
-    "            *,\n",
-    "            drop_variables=None,\n",
-    "        ):\n",
-    "            \n",
-    "            return my_open_dataset(filename_or_obj, drop_variables=drop_variables)\n",
+    "        return my_open_dataset(filename_or_obj, drop_variables=drop_variables)\n",
     "\n",
-    "   ```"
+    "```"
    ]
   },
   {
@@ -41,20 +41,18 @@
     "Declare this class as an external plugin in your `setup.py`:\n",
     "\n",
     "```python\n",
-    "    setuptools.setup(\n",
-    "        ...\n",
-    "        entry_points={\n",
-    "            'xarray.backends': ['engine_name=package.module:my_backendentrypoint'],\n",
-    "        },\n",
-    "    )\n",
-    "\n",
+    "setuptools.setup(\n",
+    "    ...\n",
+    "    entry_points={\n",
+    "        'xarray.backends': ['engine_name=package.module:my_backendentrypoint'],\n",
+    "    },\n",
+    ")\n",
     "```\n",
     "or pass it in `xr.open_dataset`:\n",
     "\n",
     "```python\n",
-    "    xr.open_dataset(..., engine=MyBackendEntrypoint)\n",
-    "```\n",
-    "<br/>"
+    "xr.open_dataset(..., engine=MyBackendEntrypoint)\n",
+    "```"
    ]
   },
   {