Adds unused dependencies check to CI

[antedeguemon]

This PR adds a new step to CI to ensure no unused dependency is locked by mix.lock.

[coveralls]

Pull Request Test Coverage Report for Build a00ad81642d967e835cf31ac3de3c846487c87a1-PR-33

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 94.623%

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Totals
Change from base Build c7b3eff25e725bb838a24b334bfbdc1528fe11c0:	0.0%
Covered Lines:	915
Relevant Lines:	967

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💛 - Coveralls