Fix: pr builds to not have access to the user credentials for github api access -> use dummy version number for pr build

.appveyor/gitDescribe.ps1

@@ -1,3 +1,9 @@
+if($Env:APPVEYOR_PULL_REQUEST_NUMBER)
+{
+	$Env:VersionTag = "0.0.0.pr-na-PR_$Env:APPVEYOR_PULL_REQUEST_NUMBER"
+	Return $Env:VersionTag
+}
+
 $currentCommitSha = $Env:CurrentCommitSha
 $githubRepoApiUri = $Env:githubRepoApiUri #"https://api.github.com/repos/:user/:repo/"
 $Env:VersionTag = ""
@@ -53,12 +59,5 @@ if(!$latestTag){
 	Return ;
 }
 
-if($Env:APPVEYOR_PULL_REQUEST_NUMBER)
-{
-	$Env:VersionTag = "$($latestTag.tag)-$($latestTag.dist)-PR_$Env:APPVEYOR_PULL_REQUEST_NUMBER"
-}
-else
-{
-    $Env:VersionTag = "$($latestTag.tag)-$($latestTag.dist)-g$($currentCommitSha.Substring(0,7))"
-}
+$Env:VersionTag = "$($latestTag.tag)-$($latestTag.dist)-g$($currentCommitSha.Substring(0,7))"
 Return $Env:VersionTag