Update nesbot/carbon requirement from ^1.25 to ^2.20

[dependabot-preview]

Updates the requirements on nesbot/carbon to permit the latest version.

Release notes

Sourced from nesbot/carbon's releases.

2.20.0

Complete commits list: briannesbitt/Carbon@2.19.1...2.20.0

Summary:

• #1745 CarbonPeriod::overlaps() method and method to create CarbonPeriod from Carbon/CarbonImmutable instances
• #1746 More generic methods is, next, previous getting strings such as "sunday", "1 July" and automatically isXyz(), nextXyz() and previousXyz() if it matches the given string.
• #1748 Support Laravel event dispatcher's contract thanks to @​lorisleiva
• #1753 Implement CarbonInterval::shares (like times but to divide) and multiply/divide method that return precise and cascaded results.

Commits

• bc671b8 Update FUNDING.yml
• f056095 Update ISSUE_TEMPLATE.md
• 9cbaca5 Merge pull request #1754 from kylekatarnls/feature/fix-1751-phpdoc-typing
• 2dcbfdb Compare only years for negative values
• 68e444b Use UTC for negative years in tests
• b40ab37 Add tests
• 25c91da Allow years before 0 and after 9999 for ->toISOString()
• 31d8f16 Fix #1751 return static type in PHPDoc
• d12b479 Fix #1750 Implement precise multiply and divide (#1753)
• 8ecbc1a Add translation author of #1749
• Additional commits viewable in compare view

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