ci: remove code coverage test & uniform file names

[SteveLauC]

Standards checklist:

• The PR title is descriptive.
• I have read CONTRIBUTING.md
• The code compiles (cargo build)
• The code passes rustfmt (cargo fmt)
• The code passes clippy (cargo clippy)
• The code passes tests (cargo test)
• Optional: I have tested the code myself

For new steps

• Optional: Topgrade skips this step where needed
• Optional: The --dry-run option works with this step
• Optional: The --yes option works with this step if it is supported by
  the underlying command

If you developed a feature or a bug fix for someone else and you do not have the
means to test it, please tag this person here.

What does this PR do

1. Remove the checks for test coverage because Topgrade is hard to have fully covered unit tests, and I think unit tests won't help that much, IMHO, we need a BDD test framework. Though I think this is also hard to do. cc @niStee

2. Unforim the names of the CI files

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