feat: change response type of health check

Author: yuseok0215

…gil/bitnagil_backend/TestController.java …nagil_backend/HealthCheckController.javasrc/main/java/bitnagil/bitnagil_backend/TestController.java renamed to src/main/java/bitnagil/bitnagil_backend/HealthCheckController.java src/main/java/bitnagil/bitnagil_backend/TestController.java renamed to src/main/java/bitnagil/bitnagil_backend/HealthCheckController.java

@@ -1,13 +1,14 @@
 package bitnagil.bitnagil_backend;
 
+import org.springframework.http.ResponseEntity;
 import org.springframework.web.bind.annotation.GetMapping;
 import org.springframework.web.bind.annotation.RestController;
 
 @RestController
-public class TestController {
+public class HealthCheckController {
 
     @GetMapping("/health-check")
-    public String newURI() {
-        return "Github Actions로 배포 성공";
+    public ResponseEntity<String> health() {
+        return ResponseEntity.ok("OK");
     }
 }