Trim whitespace from input values & cleanup

[codemasher]

Hey, this PR trims the whitespace from input values and explicitly checks against an empty string '' so that falsey values may pass - the empty() check here would fail on a string value of 0:

https://github.com/hansott/psr7-cookies/blob/fdd4790274996a3d5a723fa32d1c82e2b319e8fc/src/SetCookie.php#L171

Further I did some cleanup and updated the GH Actions workflow run (removed the low/high dependency stuff - the only call was to "locked" without a lock file).