Publishing to the Open VSIX Gallery fails on main builds

[nils-a]

because GitVersion calculated

{
  // ...
  "PreReleaseNumber": null,
  // ...
  "MajorMinorPatch": "0.1.0",
  // ...
}

and the version to be set in the vsixmanifest is $"{gitVersion.MajorMinorPatch}.{gitVersion.PreReleaseNumber}" which results in a non-valid version number.