Add codecov to CI

[mtrezza]

New Issue Checklist

• I am not disclosing a vulnerability.
• I am not just asking a question.
• I have searched through existing issues.
• I can reproduce the issue with the latest version of Parse Server and the Parse PHP SDK.

Issue Description

Codecov is missing in the CI jobs list, even though it is being performed in the CI workflow.

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[dplewis]

What exactly is the issue here?

[mtrezza]

There used to be codecov entries in the CI list, but for some reason I can't seem to find them anywhere anymore, not even in the other repos. So I'm closing.