Add cache-mode to all GitHub Actions workflows

[absidue]

Pull Request Type

• Security improvement

Description

GitHub recently added a new cache-mode key for GitHub Actions workflows that allows us to control which level of cache access each workflow and job should have ranging from read and write access, to read-only access all the way to no access. This pull request sets cache-mode: none in all workflows at the workflow level and adds overrides for the individual jobs that actually need read-only or read and write access, which is the same approach that we use for the permissions key that configures the GITHUB_TOKEN permissions.

References:

• Documentation: https://docs.github.com/en/actions/reference/workflows-and-actions/workflow-syntax#cache-mode
• Announcement: https://github.blog/changelog/2026-09-10-control-github-actions-cache-access-with-cache-mode/
• Thread explaining why it is necessary (apparently caching uses a different API token than the GITHUB_TOKEN so it doesn't respect the permissions key): https://github.com/orgs/community/discussions/194493

Testing

Successful build workflow: https://github.com/absidue/FreeTube/actions/runs/34995688123
The lint workflow on this pull request

Desktop

• OS: Windows
• OS Version: 11