chore: fix typo in the cross validation notebook (#1069)

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Author: shobsi

notebooks/ml/bq_dataframes_ml_cross_validation.ipynb

@@ -272,7 +272,7 @@
  "cell_type": "markdown",
  "metadata": {},
  "source": [
- "## 2.1 Define KFold class and Train/Test for Each Fold (Mauanl Approach)"
+ "## 2.1 Define KFold class and Train/Test for Each Fold (Manual Approach)"
  ]
  },
  {