Use typing cast for HolidayBase::__eq__

[arkid15r]

Proposed change

Resolves #1427

Use typing cast for HolidayBase::eq
Fix Unsupported operand types for == ("Mapping" and "HolidayBase") error.
Bump mypy version from 1.4.1 to v 1.5.0

Type of change

• New country/market holidays support (thank you!)
• Supported country/market holidays update (calendar discrepancy fix, localization)
• Existing code/documentation/test/process quality improvement (best practice, cleanup, refactoring, optimization)
• Dependency update (version deprecation/upgrade)
• Bugfix (non-breaking change which fixes an issue)
• Breaking change (a code change causing existing functionality to break)
• New feature (new python-holidays functionality in general)

Checklist

• I've followed the contributing guidelines
• This PR is filed against beta branch of the repository
• This PR doesn't contain any merge conflicts and has clean commit history
• The code style looks good: make pre-commit
• All tests pass locally: make test, make tox (we strongly encourage adding tests to your code)
• The related documentation has been added/updated (check off the box for free if no updates is required)

[coveralls]

Pull Request Test Coverage Report for Build 5862496579

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 100.0%

---

Totals
Change from base Build 5788118002:	0.0%
Covered Lines:	9109
Relevant Lines:	9109

---

💛 - Coveralls

[KJhellico]

LGTM.