[workflow] only report coverage for changed files

[FrankLeeeee]

Issue Number

Fixed #2530 .

What does this PR do?

This PR modified the behavior of the test coverage report in CI. It only reports coverage rate for the changed files in a PR now so that the develop knows whether his/her changes are tested sufficiently. A sample report is given below.

[github-actions]

Your pre-commit check failed, follow the steps to run pre-commit on your file for code style consistency.

1. install pre-commit via "pip install pre-commit"
2. install pre-commit hooks via "pre-commit install"
3. run pre-commit on file with format error via "pre-commit run --files path" by replacing "path" with the actual file path
4. commit and push to your branch

View your job at https://github.com/hpcaitech/ColossalAI/actions/runs/4039789704.
Read our "CONTRIBUTING.md" for more reference to the code style.

[github-actions]

Your pre-commit check failed, follow the steps to run pre-commit on your file for code style consistency.

1. install pre-commit via "pip install pre-commit"
2. install pre-commit hooks via "pre-commit install"
3. run pre-commit on file with format error via "pre-commit run --files path" by replacing "path" with the actual file path
4. commit and push to your branch

View your job at https://github.com/hpcaitech/ColossalAI/actions/runs/4039797950.
Read our "CONTRIBUTING.md" for more reference to the code style.

[FrankLeeeee]

The code coverage for the changed files is 15%

Click me to view the complete report

Name                                                                                                 Stmts   Miss  Cover
------------------------------------------------------------------------------------------------------------------------
tests/test_auto_parallel/test_tensor_shard/test_shape_consistency_pass.py                               75     75     0%
tests/test_auto_parallel/test_tensor_shard/test_solver_with_resnet_v2.py                                55     55     0%
------------------------------------------------------------------------------------------------------------------------
TOTAL                                                                                                42886  36429    0%

[FrankLeeeee]

The comment above is the sample report provided by this CI. It will only include the report for changed files.