feat: add explicit check against codeCoverage.expectFrontendCoverageOnly before attempting to collect backend coverage

[funkadelic]

PR for https://github.com/cypress-io/code-coverage/issues/473. See https://github.com/cypress-io/code-coverage/issues/473 for details behind the change

[CLAassistant]

All committers have signed the CLA.

[rsudarson]

Please release a version with this change. @maartencardinaels @funkadelic

[jogelin]

@funkadelic is this PR still planned? My monitoring is showing all of these failing requests...

[funkadelic]

@maartencardinaels thanks for the PR approval; is there anything else needed from my end to get this merged down to master & released?

[mcaverick]

@maartencardinaels thanks for the PR approval; is there anything else needed from my end to get this merged down to master & released?

one of the project collaborators will have to merge this PR

[eulersson]

Could this be revisited? What steps are required to get it through?

[eulersson]

I forked from master and brought in the same changes @funkadelic has. Therefore the PR I created is an updated duplicate of this PR.

https://github.com/cypress-io/code-coverage/pull/555