Bump pygal from 3.0.5 to 3.1.0 (#5155)

Bumps [pygal](https://github.com/Kozea/pygal) from 3.0.5 to 3.1.0.
- [Release notes](https://github.com/Kozea/pygal/releases)
- [Changelog](https://github.com/Kozea/pygal/blob/master/docs/changelog.rst)
- [Commits](Kozea/pygal@3.0.5...3.1.0)

---
updated-dependencies:
- dependency-name: pygal
  dependency-version: 3.1.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

requirements.txt

@@ -295,7 +295,7 @@ pycparser==2.23
     # via cffi
 pydyf==0.12.1
     # via weasyprint
-pygal==3.0.5
+pygal==3.1.0
     # via geotrek (setup.py)
 pymemcache==4.0.0
     # via geotrek (setup.py)