Upgrade holidays to 0.9.7

[fabaff]

Description:

Changes: https://github.com/dr-prodigy/python-holidays/blob/master/CHANGES

Example entry for configuration.yaml (if applicable):

binary_sensor:
  - platform: workday
    country: DE
  - platform: workday
    country: CH
  - platform: workday
    country: US

Checklist:

• The code change is tested and works locally.
• Local tests pass with tox. Your PR cannot be merged unless tests pass

If the code communicates with devices, web services, or third-party tools:

• New dependencies have been added to the REQUIREMENTS variable (example).
• New dependencies have been added to requirements_all.txt by running script/gen_requirements_all.py.