[해결 방법] Java8 버전 사용하고 싶으신 분들은 아래와 같이 설정하시면 됩니다.

build.gradle

plugins {
    id 'java'
    id 'org.springframework.boot' version '2.3.12.RELEASE'
    id 'io.spring.dependency-management' version '1.0.10.RELEASE'
}

group = 'com.spring.www'
version = '0.0.1-SNAPSHOT'

java {
    sourceCompatibility = JavaVersion.VERSION_1_8
    targetCompatibility = JavaVersion.VERSION_1_8
}

repositories {
    mavenCentral()
}

dependencies {
    implementation 'org.springframework.boot:spring-boot-starter-data-jpa'
    runtimeOnly 'mysql:mysql-connector-java:8.0.32'
    testImplementation 'org.springframework.boot:spring-boot-starter-test'
    testRuntimeOnly 'org.junit.platform:junit-platform-launcher'
}

tasks.named('test') {
    useJUnitPlatform()
}

gradle-wrapper.properties

distributionBase=GRADLE_USER_HOME
distributionPath=wrapper/dists
distributionUrl=https\://services.gradle.org/distributions/gradle-6.8.3-bin.zip
networkTimeout=10000
validateDistributionUrl=true
zipStoreBase=GRADLE_USER_HOME
zipStorePath=wrapper/dists