chore: convert IsAbs

Signed-off-by: Christopher Phillips <32073428+spiffcs@users.noreply.github.com>

syft/format/common/spdxhelpers/to_format_model.go

@@ -845,9 +845,10 @@ func trimPatchVersion(semver string) string {
 // with the root of the package archive or directory
 func convertAbsoluteToRelative(absPath string) (string, error) {
 	// Ensure the absolute path is absolute (although it should already be)
-	absPath, err := filepath.Abs(absPath)
-	if err != nil {
-		return "", fmt.Errorf("error converting absPath to absolute path: %v", err)
+	if !filepath.IsAbs(absPath) {
+		// already relative
+		log.Debugf("%s is already relative", absPath)
+		return absPath, nil
 	}
 
 	// we use "/" here given that we're converting absolute paths from root to relative