Better error information for failed reports when processing coverage reports

Release notes

Problem to solve

Based on #406500 (comment 1853737592)

From what I understand from what @duncan_harris is asking for is that sometimes the code coverage report that is uploaded doesn't work, and we don't have a good way of informing the user why it didn't work. I don't think we have any tooling around this to let users test their reports to validate that they will work as expected.

Proposal

Intended users

Feature Usage Metrics

Does this feature require an audit event?

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