Replace strings.SplitN with strings.Cut

Cut is a cleaner & more performant api relative to SplitN(_, _, 2) added in go 1.18

Previously applied this refactoring to buildah:
https://github.com/containers/buildah/pull/5239

Signed-off-by: Philip Dubé <philip@peerdb.io>

pkg/copy/parse.go

@@ -40,9 +40,9 @@ func parseUserInput(input string) (container string, path string) {
 		return
 	}
 
-	if spl := strings.SplitN(path, ":", 2); len(spl) == 2 {
-		container = spl[0]
-		path = spl[1]
+	if parsedContainer, parsedPath, ok := strings.Cut(path, ":"); ok {
+		container = parsedContainer
+		path = parsedPath
 	}
 	return
 }