Update dependency django-maintenance-mode to ^0.18.0

This MR contains the following updates:

Package	Type	Update	Change
django-maintenance-mode	dependencies	minor	^0.16.3 -> ^0.18.0

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Release Notes

fabiocaccamo/django-maintenance-mode

v0.18.0

Compare Source

• Drop Python < 3.8 and Django < 2.2 support. #​99
• Add backend for using default static storage ("maintenance_mode.backends.StaticStorageBackend"). (by @​matmair in #​97)
• Replace str.format with f-strings.
• Replace setup.py test in favor of runtests.py.
• Bump requirements, Github actions and pre-commit hooks.

v0.17.1

Compare Source

• Add Python 3.11 support.
• Add Django 4.1 support.
• Add pre-commit.
• Bump GitHub actions.
• Improve maintenance_mode.backends extendibility.
• Fix settings.MAINTENANCE_MODE_STATE_FILE_PATH not working with pathlib.Path value. #​96

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