Merge bitcoindevkit/bdk-cli#58: Update codecov to grcov from Tarpauline

f8200a160b4dddc96ef7478cb2ccdf5f45cfcd4a Update codecov to grcov from Tarpauline (rajarshimaitra)

Pull request description:

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  ### Description

  To match with existing codecov of BDK, Tarpaulin based codecov in bdk-cli is changed to grcov.

  ### Notes to the reviewers

  <!-- In this section you can include notes directed to the reviewers, like explaining why some parts
  of the PR were done in a specific way -->

  ### Checklists

  #### All Submissions:

  * [x] I've signed all my commits
  * [x] I followed the [contribution guidelines](https://github.com/bitcoindevkit/bdk-cli/blob/master/CONTRIBUTING.md)
  * [x] I ran `cargo fmt` and `cargo clippy` before committing

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Tree-SHA512: 8cc31829e61fffe61815c8e8cb25e9c1b1722a2f0a42f7e1c032688f8e6953f9844977bbb829eaf4499e7c3fce04f8b61f830d8c24e8481623bbc1111d0f07d2