Add week of year to gt_cache circleci cache key

[mcgibbon]

Purpose

Caching of gt4py caches on CircleCI currently only invalidates the cache if the gt4py version changes. However, caches become unusable as soon as code changes.

This PR updates the caching so that caches invalidate weekly. This should ensure that caches are at least valid on main at the start of the week, and speed up test execution, at the cost of needing to rebuild the caches at the start of the week.

Infrastructure changes:

• Updated CircleCI gt4py cache caching so that caches invalidate weekly

Checklist

Before submitting this PR, please make sure:

• You have followed the coding standards guidelines established at Code Review Checklist.
• Docstrings and type hints are added to new and updated routines, as appropriate
• All relevant documentation has been updated or added (e.g. README, CONTRIBUTING docs)
• For each public change and fix in pace-util, HISTORY has been updated

[mcgibbon]

Didn't improve test time by much because it turns out we aren't changing the computational code much right now. May merge later when we continue refactoring computational code.