Update pyyaml requirement from <5.4,>=5.3 to >=5.3,<6.1

Updates the requirements on [pyyaml](https://github.com/yaml/pyyaml) to permit the latest version.
- [Release notes](https://github.com/yaml/pyyaml/releases)
- [Changelog](https://github.com/yaml/pyyaml/blob/main/CHANGES)
- [Commits](yaml/pyyaml@5.3...6.0.2)

---
updated-dependencies:
- dependency-name: pyyaml
  dependency-type: direct:production
...

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

requirements.txt

@@ -21,7 +21,7 @@ Jinja2>=2.10,<2.11  # http://jinja.pocoo.org/docs/latest/changelog/
 MarkupSafe==2.0.1
 
 # Only for some importers:
-pyyaml>=5.3,<5.4  # http://pyyaml.org/wiki/PyYAML
+pyyaml>=5.3,<6.1  # http://pyyaml.org/wiki/PyYAML
 
 # Only for printing:
 pycups==2.0.4  # https://pypi.python.org/pypi/pycups