Bump pyyaml from 5.3 to 5.4 in /tests

Bumps [pyyaml](https://github.com/yaml/pyyaml) from 5.3 to 5.4.
- [Release notes](https://github.com/yaml/pyyaml/releases)
- [Changelog](https://github.com/yaml/pyyaml/blob/master/CHANGES)
- [Commits](yaml/pyyaml@5.3...5.4)

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

tests/requirements.txt

@@ -36,7 +36,7 @@ pyOpenSSL==19.1.0
 pyparsing==2.4.6
 python-dateutil==2.8.1
 pywinrm==0.4.1
-PyYAML==5.3
+PyYAML==5.4
 requests==2.23.0
 requests-credssp==1.1.1
 requests-ntlm==1.1.0