Fix TokenPatternSchema pattern field validation

Empty pattern field should be considered invalid

This is fixed by replacing minItems with min_items
as described in Pydantic docs:
https://pydantic-docs.helpmanual.io/usage/schema/

spacy/schemas.py

@@ -257,7 +257,7 @@ class TokenPattern(BaseModel):
 
 
 class TokenPatternSchema(BaseModel):
-    pattern: List[TokenPattern] = Field(..., minItems=1)
+    pattern: List[TokenPattern] = Field(..., min_items=1)
 
     class Config:
         extra = "forbid"

spacy/tests/regression/test_issue6258.py

@@ -0,0 +1,14 @@
+import pydantic
+import pytest
+from pydantic import ValidationError
+from spacy.schemas import TokenPattern, TokenPatternSchema
+
+
+def test_issue6258():
+    """Test that the non-empty constraint pattern field is respected"""
+    # These one is valid
+    TokenPatternSchema(pattern=[TokenPattern()])
+    # But an empty pattern list should fail to validate
+    # based on the schema's constraint
+    with pytest.raises(ValidationError):
+        TokenPatternSchema(pattern=[])