feat: don't overwrite flutter if correct version already present

[RyanCarrier]

Just a simple one to make my small runs on self hosted runners go faster. CACHE_PATH includes the version so we only need to check that. The only concern would be if they set their own cache path

[bartekpacia]

Hi, thanks for the PR.

If I understand correctly, this adds a new check-cache input. Please update the action YAML file and the README accordingly.

[RyanCarrier]

Nope the check-cache is the id of the workflow step, so the next step we can choose to not redownload flutter if it'a already there. No user facing changes