chore(deps): Update firebase/php-jwt requirement from ^5.2 to ^6.1

Created by: dependabot[bot]

Updates the requirements on firebase/php-jwt to permit the latest version.

Release notes

Sourced from firebase/php-jwt's releases.

v6.1.0

Note: There should be no issues with backwards compatibility unless types were being used incorrectly

• This version is compatible with PHP >= 7.1
• Drop support for PHP 5.3, 5.4, 5.5, 5.6, and 7.0
• Add parameter typing and return types
• Better PHPDoc / IDE support

Commits

• fbb2967 chore: update CHANGELOG for v6.1.0
• 5bbc90c chore: add back timestamp var for compatibility (#412)
• 52943f5 feat: add back compatibility for >= PHP 7.1 (#405)
• 92aa12d chore: update library to phpstan level 7 (#407)
• 13082f8 chore: add phpstan for static analysis (#406)
• e41b22a chore: add array casting to README (#402)
• 958938b chore: remove phpunit shim (#401)
• f8550f8 feat: add typing, require PHP 8.0 (#385)
• 8bcbcf8 chore(docs): fix release URL in README (#394)
• 7e0a273 fix: use property_exists for checking key id (#395)
• Additional commits viewable in compare view

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