Fix linter errors

golangci-lint upgrade to v1.56.2 added more checks

Relates to pion/.goassets#201

sdp.go

@@ -541,7 +541,7 @@ type mediaSection struct {
 
 func bundleMatchFromRemote(matchBundleGroup *string) func(mid string) bool {
 	if matchBundleGroup == nil {
-		return func(midValue string) bool {
+		return func(string) bool {
 			return true
 		}
 	}