Update Drupal core requirement - version constraint >=^8: Invalid version string "^8"

@ericrubino Thanks for catching the issue.

Changed two files: composer.json and usajobs.info.yml.

In the composer.json file, the requirement for the drupal/core package is being changed. Originally, the requirement was for any version of Drupal 8 or higher (">=^8"). The updated requirement is for any version of Drupal 8, 9, or 10 ("^8 || ^9 || ^10"). This means the code is compatible with these specific major versions of Drupal.

In the usajobs.info.yml file, a similar change is being made to the core_version_requirement. Originally, the module could run on any version of Drupal 8 or higher. The updated requirement is for any version of Drupal 8, 9, or 10.