Fix for a tiny typo in _MinLengthValidator (#1209)

* tiny typo fix for min length validator's error string

* [pre-commit.ci] auto fixes from pre-commit.com hooks

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Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

src/attr/validators.py

@@ -550,7 +550,7 @@ def __call__(self, inst, attr, value):
         We use a callable class to be able to change the ``__repr__``.
         """
         if len(value) < self.min_length:
-            msg = f"Length of '{attr.name}' must be => {self.min_length}: {len(value)}"
+            msg = f"Length of '{attr.name}' must be >= {self.min_length}: {len(value)}"
             raise ValueError(msg)
 
     def __repr__(self):