Polish "Use non-deprecated syntax to configure sourceCompatibility"

See gh-47339

Author: snicoll

buildSrc/src/test/java/org/springframework/boot/build/ConventionsPluginTests.java

@@ -76,7 +76,9 @@ void jarIncludesLegalFiles() throws IOException {
 			out.println("    id 'org.springframework.boot.conventions'");
 			out.println("}");
 			out.println("version = '1.2.3'");
-			out.println("sourceCompatibility = '17'");
+			out.println("java {");
+			out.println("    sourceCompatibility = '17'");
+			out.println("}");
 			out.println("description 'Test project for manifest customization'");
 			out.println("jar.archiveFileName = 'test.jar'");
 		}
@@ -106,7 +108,9 @@ void sourceJarIsBuilt() throws IOException {
 			out.println("    id 'org.springframework.boot.conventions'");
 			out.println("}");
 			out.println("version = '1.2.3'");
-			out.println("sourceCompatibility = '17'");
+			out.println("java {");
+			out.println("    sourceCompatibility = '17'");
+			out.println("}");
 			out.println("description 'Test'");
 		}
 		runGradle("assemble");
@@ -135,7 +139,9 @@ void javadocJarIsBuilt() throws IOException {
 			out.println("    id 'org.springframework.boot.conventions'");
 			out.println("}");
 			out.println("version = '1.2.3'");
-			out.println("sourceCompatibility = '17'");
+			out.println("java {");
+			out.println("    sourceCompatibility = '17'");
+			out.println("}");
 			out.println("description 'Test'");
 		}
 		runGradle("assemble");