Polish "Write Gradle plugin repositories section only if necessary"

See gh-880

initializr-generator/src/test/java/io/spring/initializr/generator/buildsystem/gradle/KotlinDslGradleSettingsWriterTests.java

@@ -42,6 +42,13 @@ class KotlinDslGradleSettingsWriterTests {
 				"        gradlePluginPortal()", "    }", "}");
 	}
 
+	@Test
+	void gradleBuildWithoutPluginRepository() throws IOException {
+		GradleBuild build = new GradleBuild();
+		List<String> lines = generateSettings(build);
+		assertThat(lines).doesNotContain("pluginManagement");
+	}
+
 	@Test
 	void gradleBuildWithPluginRepository() throws IOException {
 		GradleBuild build = new GradleBuild();