[BUG] df.loc[:] generates a different index_value key from original one

[qinxuye]

Describe the bug

df.loc[:] generates a different index_value key from df.index_value.key.

To Reproduce
To help us reproducing this bug, please provide information below:

1. Your Python version
2. The version of Mars you use
3. Versions of crucial packages, such as numpy, scipy and pandas
4. Full stack of the error.
5. Minimized code to reproduce the error.

In [1]: import mars.tensor as mt

In [2]: import mars.dataframe as md

In [3]: df = md.DataFrame(mt.random.rand(10, 4), chunk_size=4, index=md.date_ran
   ...: ge('2022-1-1', periods=10))

In [4]: df2 = df.loc[:]

In [5]: df.index_value.key
Out[5]: 'f1f137ddfd28afb3bc0cbece9e232cc0'

In [6]: df2.index_value.key
Out[6]: '6ff9bd78bc9d0f7fbbe9717588296ceb'  # different