Have lycheeVersion: latest to use the current lychee release

[tooomm]

As discussed earlier in a related ticket to lycheeverse/lychee#1212:
#203

See comments following #203 (comment), including a proposed logic by @kemingy.

This could be a good standard setting for the action in general and can get rid of constant manual version bumps to stay en par with the main tool (e.g. ebd95eb).

[mre]

Wouldn't this update the lychee version even for users who've pinned the lychee-action? This could potentially introduce breaking changes unexpectedly.

I'm not entirely sure how GitHub Actions handle this interaction between action versions and tool versions.

[mre]

@tooomm, any thoughts?