Minor improvement to regular expression.

Author: Malcolmnixon

src/DemaConsulting.SpdxModel/SpdxElement.cs

@@ -31,7 +31,7 @@ public abstract class SpdxElement
     /// Regular expression for checking element IDs of the form "SPDXRef-name"
     /// </summary>
     protected static readonly Regex SpdxRefRegex = new(
-        "SPDXRef-[a-zA-Z0-9-,]+",
+        "^SPDXRef-[a-zA-Z0-9,-]+$",
         RegexOptions.None,
         TimeSpan.FromMilliseconds(100));