Drop testing on macOS 10

[kousu]

Checklist

GitHub

• I've given this PR a concise, self-descriptive, and meaningful title
• I've linked relevant issues in the PR body
• I've applied the relevant labels to this PR
• I've assigned a reviewer

PR contents

• I've consulted ivadomed's internal developer documentation to ensure my contribution is in line with any relevant design decisions
• I've added relevant tests for my contribution
• I've updated the relevant documentation for my changes, including argparse descriptions, docstrings, and ReadTheDocs tutorial pages

Description

See actions/runner-images#5583

We should perhaps later re-add "macos-11" when "macos-latest" becomes "macos-12"

[kousu]

(The lack of) This just blocked #1137 in https://github.com/ivadomed/ivadomed/actions/runs/2791716988:

[coveralls]

Pull Request Test Coverage Report for Build 2791911499

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 increased (+0.2%) to 69.353%

---

Totals
Change from base Build 2771735045:	0.2%
Covered Lines:	4277
Relevant Lines:	6167

---

💛 - Coveralls

[kanishk16]

This was long overdue... Thanks for taking care of this!