Track spec coverage with codecov

[elia]

Summary

• Coverage is reported for the sandbox/ dir (I wasn't able to trick SimpleCov into believing those paths were in templates/)
• Enabled only for 3.2 which is able able track ERB files

Checklist

Check out our PR guidelines for more details.

The following are mandatory for all PRs:

• [ ] I have written a thorough PR description.
• [ ] I have kept my commits small and atomic.
• [ ] I have used clear, explanatory commit messages.

The following are not always needed:

• 📖 I have updated the README to account for my changes.
• 📑 I have documented new code with YARD.
• 🛣️ I have opened a PR to update the guides.
• ✅ I have added automated tests to cover my changes.
• 📸 I have attached screenshots to demo visual changes.

[codecov[bot]]

Codecov Report

:exclamation: No coverage uploaded for pull request base (main@7cf7e76). Click here to learn what that means. The diff coverage is n/a.

:exclamation: Current head 56fc608 differs from pull request most recent head dfd9d2a. Consider uploading reports for the commit dfd9d2a to get more accurate results

@@           Coverage Diff           @@
##             main     #329   +/-   ##
=======================================
  Coverage        ?   56.71%           
=======================================
  Files           ?      139           
  Lines           ?     2664           
  Branches        ?        0           
=======================================
  Hits            ?     1511           
  Misses          ?     1153           
  Partials        ?        0           

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