fix: the bug when auto_mount=True

[SunsetWolf]

Description

Setting auto_mount=True when using qlib.__init__ triggers an error:

• the first time you can execute it without any problem, but the second time you will get an error;
• or when you manually mount it, you execute qlib.__init__(auto_mount=True);

In both cases, you will get an error.

AttributeError: ‘str’ object has no attribute ‘decode’.

Reason:
When text=True: stdout.readlines() returns a list of str's. But decode(“utf-8”) is also called here, and str does not have a decode method, so it is reported:

Motivation and Context

How Has This Been Tested?

• Pass the test by running: pytest qlib/tests/test_all_pipeline.py under upper directory of qlib.
• If you are adding a new feature, test on your own test scripts.

Screenshots of Test Results (if appropriate):

1. Pipeline test:
2. Your own tests:

Types of changes

• Fix bugs
• Add new feature
• Update documentation