[Security] Bump pyyaml from 5.1 to 5.4.1

[dependabot-preview]

Bumps pyyaml from 5.1 to 5.4.1.

Changelog

Sourced from pyyaml's changelog.

5.4.1 (2021-01-20)

• yaml/pyyaml#480 -- Fix stub compat with older pyyaml versions that may unwittingly load it

5.4 (2021-01-19)

• yaml/pyyaml#407 -- Build modernization, remove distutils, fix metadata, build wheels, CI to GHA
• yaml/pyyaml#472 -- Fix for CVE-2020-14343, moves arbitrary python tags to UnsafeLoader
• yaml/pyyaml#441 -- Fix memory leak in implicit resolver setup
• yaml/pyyaml#392 -- Fix py2 copy support for timezone objects
• yaml/pyyaml#378 -- Fix compatibility with Jython

5.3.1 (2020-03-18)

• yaml/pyyaml#386 -- Prevents arbitrary code execution during python/object/new constructor

5.3 (2020-01-06)

• yaml/pyyaml#290 -- Use is instead of equality for comparing with None
• yaml/pyyaml#270 -- Fix typos and stylistic nit
• yaml/pyyaml#309 -- Fix up small typo
• yaml/pyyaml#161 -- Fix handling of slots
• yaml/pyyaml#358 -- Allow calling add_multi_constructor with None
• yaml/pyyaml#285 -- Add use of safe_load() function in README
• yaml/pyyaml#351 -- Fix reader for Unicode code points over 0xFFFF
• yaml/pyyaml#360 -- Enable certain unicode tests when maxunicode not > 0xffff
• yaml/pyyaml#359 -- Use full_load in yaml-highlight example
• yaml/pyyaml#244 -- Document that PyYAML is implemented with Cython
• yaml/pyyaml#329 -- Fix for Python 3.10
• yaml/pyyaml#310 -- Increase size of index, line, and column fields
• yaml/pyyaml#260 -- Remove some unused imports
• yaml/pyyaml#163 -- Create timezone-aware datetimes when parsed as such
• yaml/pyyaml#363 -- Add tests for timezone

5.2 (2019-12-02)

• Repair incompatibilities introduced with 5.1. The default Loader was changed, but several methods like add_constructor still used the old default yaml/pyyaml#279 -- A more flexible fix for custom tag constructors yaml/pyyaml#287 -- Change default loader for yaml.add_constructor yaml/pyyaml#305 -- Change default loader for add_implicit_resolver, add_path_resolver
• Make FullLoader safer by removing python/object/apply from the default FullLoader yaml/pyyaml#347 -- Move constructor for object/apply to UnsafeConstructor
• Fix bug introduced in 5.1 where quoting went wrong on systems with sys.maxunicode <= 0xffff yaml/pyyaml#276 -- Fix logic for quoting special characters
• Other PRs: yaml/pyyaml#280 -- Update CHANGES for 5.1

5.1.2 (2019-07-30)

... (truncated)

Commits

• ee37f46 5.4.1 release
• 2b37f15 Fix stub compat with older pyyaml versions that may unwittingly load it
• 58d0cb7 5.4 release
• a60f7a1 Fix compatibility with Jython
• ee98abd Run CI on PR base branch changes
• ddf2033 constructor.timezone: _copy & deepcopy
• fc914d5 Avoid repeatedly appending to yaml_implicit_resolvers
• a001f27 Fix for CVE-2020-14343
• fe15062 Add 3.9 to appveyor file for completeness sake
• 1e1c7fb Add a newline character to end of pyproject.toml
• Additional commits viewable in compare view

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[dependabot-preview]

We've just been alerted that this update fixes a security vulnerability:

Sourced from The GitHub Security Advisory Database.

Improper Input Validation in PyYAML

A vulnerability was discovered in the PyYAML library in versions before 5.3.1, 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. An attacker could use this flaw to execute arbitrary code on the system by abusing the python/object/new constructor.

Affected versions: ["< 5.3.1"]