GHA: Validate release version number

There's a reasonable chance this workflow will be triggered by a human
(via `workflow_dispatch``), and a non-zero chance with an invalid
version number for which a release should not be created.  Detect this
and provide a way for the operator to debug the source of the error.

Also fix some whitespace inconsistencies.

Signed-off-by: Chris Evich <[email protected]>