Assigning a column by attribute does not work

[rjzamora]

Came across a subtle bug/change in dask-expr while debugging a dask-cudf test:

import dask.dataframe as dd

df = dd.from_dict({"a": [0, 1]}, 1)
df.dtypes.a  # dtype('int64')

df.a = df.a.astype("float")
df.dtypes.a  # `meta` is NOT updated: dtype('int64')

df["a"] = df.a.astype("float")
df.dtypes.a  # `meta` IS updated: dtype('float64')

[phofl]

This doesn't work at all fwiw, the column isn't updated either