Use "JUnit" instead of "Junit"

See gh-17272

spring-boot-project/spring-boot-docs/src/main/asciidoc/spring-boot-features.adoc

@@ -6934,7 +6934,7 @@ useful libraries.
 
 [TIP]
 ====
-The starter also brings the vintage engine so that you can run both JUnit 4 and Junit 5
+The starter also brings the vintage engine so that you can run both JUnit 4 and JUnit 5
 tests. If you have migrated your tests to JUnit 5, you should exclude JUnit 4 support, as
 shown in the following example:
 

spring-boot-samples/spring-boot-sample-junit-jupiter/src/main/java/sample/SampleJUnitJupiterApplication.java

@@ -20,10 +20,10 @@ import org.springframework.boot.SpringApplication;
 import org.springframework.boot.autoconfigure.SpringBootApplication;
 
 @SpringBootApplication
-public class SampleJunitJupiterApplication {
+public class SampleJUnitJupiterApplication {
 
 	public static void main(String[] args) {
-		SpringApplication.run(SampleJunitJupiterApplication.class, args);
+		SpringApplication.run(SampleJUnitJupiterApplication.class, args);
 	}
 
 }

spring-boot-samples/spring-boot-sample-junit-jupiter/src/test/java/sample/SampleJUnitJupiterApplicationTests.java

@@ -26,7 +26,7 @@ import org.springframework.boot.test.web.client.TestRestTemplate;
 import static org.assertj.core.api.Assertions.assertThat;
 
 @SpringBootTest(webEnvironment = WebEnvironment.RANDOM_PORT)
-class SampleJunitJupiterApplicationTests {
+class SampleJUnitJupiterApplicationTests {
 
 	@Autowired
 	private TestRestTemplate restTemplate;

spring-boot-samples/spring-boot-sample-junit-vintage/src/main/java/sample/SampleJUnitVintageApplication.java

@@ -20,10 +20,10 @@ import org.springframework.boot.SpringApplication;
 import org.springframework.boot.autoconfigure.SpringBootApplication;
 
 @SpringBootApplication
-public class SampleJunitVintageApplication {
+public class SampleJUnitVintageApplication {
 
 	public static void main(String[] args) {
-		SpringApplication.run(SampleJunitVintageApplication.class, args);
+		SpringApplication.run(SampleJUnitVintageApplication.class, args);
 	}
 
 }

spring-boot-samples/spring-boot-sample-junit-vintage/src/test/java/sample/SampleJUnitVintageApplicationTests.java

@@ -29,7 +29,7 @@ import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.
 
 @RunWith(SpringRunner.class)
 @WebMvcTest
-public class SampleJunitVintageApplicationTests {
+public class SampleJUnitVintageApplicationTests {
 
 	@Autowired
 	private MockMvc mockMvc;

src/checkstyle/checkstyle-suppressions.xml

@@ -44,5 +44,5 @@
 	<suppress files="JavaLoggingSystemTests" checks="SpringJUnit5" />
 	<suppress files="Log4J2LoggingSystemTests" checks="SpringJUnit5" />
 	<suppress files="RestClientTestWithComponentIntegrationTests" checks="SpringJUnit5" />
-	<suppress files="SampleJunitVintageApplicationTests" checks="SpringJUnit5" />
+	<suppress files="SampleJUnitVintageApplicationTests" checks="SpringJUnit5" />
 </suppressions>