chore(deps): bump org.testng:testng from 7.1.0 to 7.12.0 in /backend

Bumps [org.testng:testng](https://github.com/testng-team/testng) from 7.1.0 to 7.12.0.
- [Release notes](https://github.com/testng-team/testng/releases)
- [Changelog](https://github.com/testng-team/testng/blob/master/CHANGES.txt)
- [Commits](https://github.com/testng-team/testng/commits/7.12.0)

---
updated-dependencies:
- dependency-name: org.testng:testng
  dependency-version: 7.12.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

backend/build.gradle.kts

@@ -15,7 +15,7 @@ repositories {
 dependencies {
 	implementation("org.springframework.boot:spring-boot-starter-web")
 	implementation("org.springdoc:springdoc-openapi-starter-webmvc-ui:2.1.0")
-    implementation("org.testng:testng:7.1.0")
+    implementation("org.testng:testng:7.12.0")
 	developmentOnly("org.springframework.boot:spring-boot-devtools")
 	testImplementation("org.springframework.boot:spring-boot-starter-test")
 }