feat(asm): fix segmentation fault parsing JSON in Python2 (backport #4082)

[mergify]

This is an automatic backport of pull request #4082 done by Mergify.
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Changes to be committed:
	modified:   ddtrace/appsec/_ddwaf.pyx
	new file:   releasenotes/notes/asm-fix-python-2-error-reading-ddwaf-rules-d3653031f2ba84ba.yaml

Unmerged paths:
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	both modified:   tests/appsec/test_processor.py

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[brettlangdon]

We should resolve the merge conflict from #4094 first, and then backport that PR to 0.61.