Fix shared task dict BUG

[you-n-g]

Fix shared task dict BUG

Description

The task t is shared when generating rolling tasks.
Modification on new tasks will affect old tasks

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

[you-n-g]

We've fixed a CI error recently 509bfcb
Please rebase the PR to the main branch or merge the main branch to pass the CI test.

Thanks