fix long import

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

Author: ldetmer

java-spanner/samples/snippets/src/main/java/com/example/spanner/MutableCredentialsExample.java

@@ -40,8 +40,8 @@ static void createClientWithMutableCredentials() throws IOException {
         final String credentialsPath = "location_of_service_account_credential_json";
         Path path = Paths.get(credentialsPath);
         // Use an AtomicReference to hold the mutable lastModifiedTime so it can be accessed in the lambda
-        final java.util.concurrent.atomic.AtomicReference<FileTime> lastModifiedTime =
-                new java.util.concurrent.atomic.AtomicReference<>(Files.getLastModifiedTime(path));
+        final AtomicReference<FileTime> lastModifiedTime =
+            new AtomicReference<>(Files.getLastModifiedTime(path));
 
         // 1 - create service account credentials
         ServiceAccountCredentials serviceAccountCredentials;