Ensure that building test apps produces Java 17 bytecode

See gh-41980

spring-boot-tests/spring-boot-integration-tests/spring-boot-launch-script-tests/spring-boot-launch-script-tests-app/build.gradle

@@ -5,6 +5,11 @@ plugins {
 
 apply plugin: "io.spring.dependency-management"
 
+java {
+	sourceCompatibility = '17'
+	targetCompatibility = '17'
+}
+
 repositories {
 	maven { url "file:${rootDir}/../docker-test-maven-repository"}
 	mavenCentral()

spring-boot-tests/spring-boot-integration-tests/spring-boot-loader-classic-tests/spring-boot-loader-classic-tests-app/build.gradle

@@ -5,6 +5,11 @@ plugins {
 
 apply plugin: "io.spring.dependency-management"
 
+java {
+	sourceCompatibility = '17'
+	targetCompatibility = '17'
+}
+
 repositories {
 	maven { url "file:${rootDir}/../docker-test-maven-repository"}
 	mavenCentral()

spring-boot-tests/spring-boot-integration-tests/spring-boot-loader-tests/spring-boot-loader-tests-app/build.gradle

@@ -5,6 +5,11 @@ plugins {
 
 apply plugin: "io.spring.dependency-management"
 
+java {
+	sourceCompatibility = '17'
+	targetCompatibility = '17'
+}
+
 repositories {
 	maven { url "file:${rootDir}/../docker-test-maven-repository"}
 	mavenCentral()

spring-boot-tests/spring-boot-integration-tests/spring-boot-loader-tests/spring-boot-loader-tests-signed-jar/build.gradle

@@ -7,6 +7,11 @@ plugins {
 
 apply plugin: "io.spring.dependency-management"
 
+java {
+	sourceCompatibility = '17'
+	targetCompatibility = '17'
+}
+
 repositories {
 	maven { url "file:${rootDir}/../docker-test-maven-repository"}
 	mavenCentral()

spring-boot-tests/spring-boot-integration-tests/spring-boot-server-tests/spring-boot-server-tests-app/build.gradle

@@ -9,6 +9,11 @@ plugins {
 
 apply plugin: "io.spring.dependency-management"
 
+java {
+	sourceCompatibility = '17'
+	targetCompatibility = '17'
+}
+
 repositories {
 	maven { url "file:${rootDir}/../test-repository"}
 	mavenCentral()