- Updated the version of `@actions/github` from `6.0.0` to `6.0.1` in package.json and package-lock.json.
- Updated the version of `@octokit/core` from `6.1.5` to `7.0.3` in package.json and package-lock.json.
- Updated various dependencies in package-lock.json to their latest versions.
- Updated the last reviewed commit references and dates in all relevant stub files to reflect the latest changes in the GitHub Actions Toolkit.

Co-authored-by: Copilot <[email protected]>

This pull request introduces support for the `@actions/cache` package
for local testing, enhances the `.env.example` file with more
comprehensive documentation and variables, and updates documentation to
reflect these changes. It also adds new test stubs and minor version
bumps for toolkit dependencies.

**Local caching and environment variable enhancements:**

- Added support for the `@actions/cache` package, enabling local caching
of dependencies and files between runs by requiring the
`LOCAL_ACTION_CACHE_PATH` environment variable. Also clarified
requirements for `@actions/artifact` and `@actions/cache` in the
changelog.
- Major overhaul of `.env.example` to include detailed documentation,
default values, and grouping of variables for `@github/local-action`,
GitHub Actions inputs, and runner/environment variables. Added new
variables such as `LOCAL_ACTION_CACHE_PATH`, `LOCAL_ACTION_WORKSPACE`,
and provided more explicit defaults for local testing.

**Documentation and toolkit stub management:**

- Added instructions in `CONTRIBUTING.md` for updating toolkit stubs,
including how to track reviewed versions and compare toolkit package
changes, to ensure consistency and easier maintenance.
- Updated the supported version of `@actions/github` in the `README.md`
from `6.0.0` to `6.0.1`.

**Testing and stub improvements:**

- Added a stub for `@actions/io` in `__fixtures__/@actions/io.ts` for
use in tests, implementing mock versions of `which` and `mkdirP`.
- Added a stub for `isDebug` to the `@actions/core` test fixture.