* fixes #322 check for null

fixes #322 

ig the main issue was an api issue checking for null should work fine
otherwise we can add semver validation via regex

* chore: added better errors and comments

$HOME can change between composite-action steps on some runners
(e.g. self-hosted ones where actions/checkout temporarily overrides
it), which makes the PATH entry from the setup step point at a
different directory than the install step writes to. The result is
'lychee: command not found' even though install reported success.

$RUNNER_TEMP is guaranteed-writable and stable across steps within
a job, which is exactly what we need here.

Also drops vestigial lychee binary cleanup step.

With $RUNNER_TEMP the install directory is fresh per job, and
'install -t' overwrites existing files by default, so the explicit
'rm -f' step is no longer doing anything useful.

Fixes #337

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]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

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

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

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>