Update firebase/php-jwt dependency from v6 to v7

Problem/Motivation

The module currently requires firebase/php-jwt ^6.10, which is outdated. Version 6 is no longer receiving security updates, and composer audit flags it as a dependency that should be upgraded. Version 7 of firebase/php-jwt introduces key size validation and other security hardening improvements.

Steps to reproduce

Install the module and run composer audit
Observe that firebase/php-jwt v6 is flagged

Proposed resolution

Update the firebase/php-jwt constraint in composer.json from ^6.10 to ^7.0.

The module's existing code in NotificationsTokenService is already fully compatible with v7:

JWT::decode() already uses the new Key($secret, 'HS256') pattern introduced as required in v7
JWT::encode() signature is unchanged between v6 and v7
The module uses HS256, which is not affected by the new minimum key size enforcement (which only applies to RSA/EC keys)
The module already requires Drupal 10/11, meaning PHP 8.0+ is guaranteed, satisfying the new v7 PHP requirement
No code changes are needed — only the composer constraint needs to be loosened.

Remaining tasks

Update composer.json constraint from ^6.10 to ^7.0
Verify tests pass against firebase/php-jwt v7

User interface changes

None.

API changes

None.

Data model changes

None.