Remove requirement of PyYAML!=5.4.x

[chris-boson]

🚀 Feature

Remove dependency requirement of PyYAML!=5.4.x

Motivation

According to safety PyYAML versions below 5.4 have a security vulnerability which means that our pre-commit hooks don't allow upgrading to a newer versions of lightning.

-> pyyaml, installed 5.3.1, affected <5.4, id 39611
A vulnerability was discovered in the PyYAML library in versions before 5.4, where it is susceptible to 
arbitrary code execution when it processes untrusted YAML files through the full_load method or with 
the FullLoader loader. Applications that use the library to process untrusted input may be vulnerable 
to this flaw. This flaw allows an attacker to execute arbitrary code on the system by abusing the 
python/object/new constructor. This flaw is due to an incomplete fix for CVE-2020-1747. See CVE-2020-14343.

Pitch

Figure out why 5.4.x doesn't work for lightning and remove this requirement if possible.

[Borda]

@chris-boson mind send a PR, it shall be a quick fix

[chris-boson]

Sure, looks like I need permission to push.

[kaushikb11]

Hi @chris-boson, you would need to fork the repo and do a Pull Request to contribute.

[JMMarchant]

Any update on this?