ci: bump flat-cache from 3.2.0 to 6.1.2

Bumps [flat-cache](https://github.com/jaredwray/cacheable/tree/HEAD/packages/flat-cache) from 3.2.0 to 6.1.2.
- [Release notes](https://github.com/jaredwray/cacheable/releases)
- [Commits](https://github.com/jaredwray/cacheable/commits/HEAD/packages/flat-cache)

---
updated-dependencies:
- dependency-name: flat-cache
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>