More accurate check for YAML renderers

[mnaoumov]

I found a minor flaw in PR #638, which could behave incorrectly in an edge case

[coveralls]

Pull Request Test Coverage Report for Build 2457134641

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 4 of 4 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.001%) to 93.202%

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Totals
Change from base Build 2457016649:	0.001%
Covered Lines:	25767
Relevant Lines:	27019

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💛 - Coveralls