Fix multitarget stratification (#1308)

* data: add data for multitarget classification

* fix: prevent stratify with unbalanced classes

* test: add multitarget classification stratify test

* Automated autopep8 fixes

* fix: fix path for test data

* Automated autopep8 fixes

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Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

fedot/core/data/data_split.py

@@ -146,6 +146,16 @@ def _are_stratification_allowed(data: Union[InputData, MultiModalData], split_ra
     if test_size < labels_count:
         return False
 
+    # check that multitarget classes can be stratified
+    if data.target.ndim == 2:
+        y = np.array([" ".join(row.astype("str")) for row in data.target])
+
+        classes, y_indices = np.unique(y, return_inverse=True)
+
+        class_counts = np.bincount(y_indices)
+        if np.min(class_counts) < 2:
+            return False
+
     return True