fix unit test

Author: arturcic

src/GitVersionCore.Tests/ConfigProviderTests.cs

@@ -339,7 +339,7 @@ string SetupConfigFileContent(string text, string fileName = ConfigurationProvid
 
     string SetupConfigFileContent(string text, string fileName, string path)
     {
-        var fullPath = Path.Combine(path, fileName);
+        var fullPath = Path.GetFullPath(Path.Combine(path, fileName));
         fileSystem.WriteAllText(fullPath, text);
 
         return fullPath;