[BUG] Fix Codecov.io Base Reports for PRs

[mdemoret-nv]

Discovered while working on PR #3338, all of the PRs are currently missing their base reports (PRs can be found here). This started when we switched to a 'squash and merge' strategy for PRs. The last PR with a base report is #3340.

Without an accurate base report, many of the codecov comments are incorrect since it will be showing a report with the wrong PR base. Also, trying to view any PR comparison on codecov.io shows an error. See this and this example.

After looking into this for a bit, I believe the issue is due to the new commit SHA that is created when squashing the PR commit IDs. Since no coverage is uploaded for this new SHA, there is no coverage information in the default branch: branch-0.18.

Some potential fixes:

• Rerun CI again for the new squashed commits
  • This would be redundant, but would add in the necessary coverage information to the squashed commits
• When the ops-bot runs, coverage information from the PR Head can be copied to the new squash commit SHA
  • Not sure if this is possible due to my limited experience with the CI bots
• Find a way in codecov.io to handle the squash and merge method
  • It looks like others have run into this issue before. However, no resolution was posted.

[mdemoret-nv]

Talked with Ops today about this issue. They are looking into the potential fixes listed and will get back to me later this week.

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