Bump holidays from 0.27.1 to 0.28

Bumps [holidays](https://github.com/dr-prodigy/python-holidays) from 0.27.1 to 0.28.
- [Release notes](https://github.com/dr-prodigy/python-holidays/releases)
- [Changelog](https://github.com/dr-prodigy/python-holidays/blob/master/CHANGES)
- [Commits](dr-prodigy/python-holidays@v.0.27.1...v.0.28)

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

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

requirements.txt

@@ -4,7 +4,7 @@
 #
 #    pip-compile requirements.in
 #
-holidays==0.27.1
+holidays==0.28
     # via -r requirements.in
 python-dateutil==2.8.2
     # via