Related to #429

…to v4

Allows updating @actions/core and @actions/tool-cache. Their old versions had dependencies with security issues.

Bumps [actions/checkout](https://github.com/actions/checkout) from 5 to 6.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v5...v6)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

Google no longer serves the `tools` package: it is gone from
repository2-3.xml, so `sdkmanager tools` fails with
"Failed to find package 'tools'" and takes the whole action down with it.

- Drop `tools` from the default value of the `packages` input, leaving
  `platform-tools`. The command line tools that replaced it are already
  installed by this action, and there is no bare `cmdline-tools` package
  path to install instead (only versioned ones, e.g. `cmdline-tools;20.0`).
- Skip `tools` with a warning when it is requested explicitly, so the
  many workflows that pass `packages: 'tools platform-tools'` keep working
  instead of failing.
- Update the README accordingly.

Co-Authored-By: Claude Opus 5 <[email protected]>

Bumps [actions/checkout](https://github.com/actions/checkout) from 6 to 7.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v6...v7)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-version: '7'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

Old versions are using deprecated Node.js version