fix: return the raw error from Argument.Get

There are other places in the logic that depend on errors extracting Argument values being of type ParameterNodeError specifically, so we shouldn't wrap these errors further.

internal/hook/hook.go

@@ -1092,7 +1092,7 @@ func (r SignatureRule) Evaluate(req *Request) (bool, error) {
 	// find the signature
 	sig, err := r.Signature.Get(req)
 	if err != nil {
-		return false, fmt.Errorf("could not extract signature string: %w", err)
+		return false, err
 	}
 
 	// determine the payload that is signed