Auto merge of #13767 - epage:msrv-test, r=ehuss

test(msrv): Re-organize MSRV tests

### What does this PR try to resolve?

- Merge test cases
- Clarify names
- Focus on `cargo tree`, rather than `cargo check` (faster and more to
  what we are testing)

### How should we test and review this PR?

### Additional information

Author: bors