[BUG] `astype` on pandas nullable string type seems to be not returning the correct type

**Describe the bug**
`astype` on pandas nullable string type seems to be not returning the correct type. This is the cause for failures in:
`pandas-testing/pandas-tests/tests/extension/test_arrow.py::TestArrowArray::test_astype_string`

**Steps/Code to reproduce bug**
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**Expected behavior**
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**Environment overview (please complete the following information)**
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**Environment details**
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**Additional context**
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