Fix flipped condition

Author: filipnavara

src/NerdBank.GitVersioning/ManagedGit/GitRepository.cs

@@ -686,7 +686,7 @@ private static bool TryConvertHexStringToByteArray(string hexString, out byte[]?
             for (int index = 0; index < data.Length; index++)
             {
                 string byteValue = hexString.Substring(index * 2, 2);
-                if (byte.TryParse(byteValue, NumberStyles.HexNumber, CultureInfo.InvariantCulture, out data[index]))
+                if (!byte.TryParse(byteValue, NumberStyles.HexNumber, CultureInfo.InvariantCulture, out data[index]))
                 {
                     data = null;
                     return false;