Update publish-new-version.yaml (#5691)

Add more details about the how the version should be formatted. 

When trying to run this workflow, I'm always very unsure whether the
version should be prepended with a `v` or not. This should be clearly
stated in the description. If it doesn't matter, that should also be
stated explicitly.

Updated the texts after talking to @chriswk and making a release.

.github/workflows/publish-new-version.yaml

@@ -11,7 +11,7 @@ on:
   workflow_dispatch:
     inputs:
       version:
-        description: What version would you like to use?
+        description: What version number would you like to use? The version number should be **without** a leading `v`, e.g. `5.7.1` or `6.2.4`.
 
 jobs:
   build: