This is unrelated to your YAML problem...

Do you mind a mini-review of your code?

To get your SYNOPSIS POD to render as code, you should indent as follows:

=head1 SYNOPSIS

    use Test::Regression;
    ok_regression(sub {return "hello world"}, "t/out/hello_world.txt")
+;
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You should explicitly mention that TEST_REGRESSION_GEN is an environment variable:

If the TEST_REGRESSION_GEN environment variable is set to a true value
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Additionally, I recommend adding a DESCRIPTION section to briefly discuss why someone would use your module. How would I distinguish it from the other CPAN Test modules? Does it complement other Test modules?