DOC: infer_dtypes document is inconsistent with behaviour regarding boolean
#### Location of the documentation

https://github.com/pandas-dev/pandas/blob/0711b7adb3150f14461c5d1a111a87a83a45bc90/pandas/_libs/lib.pyx#L1315


#### Documentation problem

In this example the return value should be 'boolean' as mentioned in this test case https://github.com/pandas-dev/pandas/blob/1db3aa2b8ae8bd3b20dea14b92e1e7355bfa266a/pandas/tests/dtypes/test_inference.py#L679

#### Suggested fix for documentation

change 'mix' to 'boolean'
