Bump pyyaml from 5.3.1 to 5.4 in /.github/workflows

Bumps [pyyaml](https://github.com/yaml/pyyaml) from 5.3.1 to 5.4.
- [Release notes](https://github.com/yaml/pyyaml/releases)
- [Changelog](https://github.com/yaml/pyyaml/blob/master/CHANGES)
- [Commits](yaml/pyyaml@5.3.1...5.4)

Signed-off-by: dependabot[bot] <support@github.com>

.github/workflows/mkdocs-requirements.txt

@@ -12,7 +12,7 @@ mkdocs-material-extensions==1.0
 Pygments==2.6.1
 pymdown-extensions==8.0
 python-dateutil==2.8.1
-PyYAML==5.3.1
+PyYAML==5.4
 repackage==0.7.3
 six==1.15.0
 termcolor==1.1.0