Refine SpringBootTest.useMainMethod support

Refine `SpringBootContextLoader` so that calls to the main method do
not exit early and the hook is only used when necessary.

See gh-22405

spring-boot-tests/spring-boot-smoke-tests/spring-boot-smoke-test-data-ldap/src/test/java/smoketest/data/ldap/SampleLdapApplicationTests.java

@@ -20,6 +20,7 @@ import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.extension.ExtendWith;
 
 import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.boot.test.context.SpringBootTest.UseMainMethod;
 import org.springframework.boot.test.system.CapturedOutput;
 import org.springframework.boot.test.system.OutputCaptureExtension;
 
@@ -31,7 +32,7 @@ import static org.assertj.core.api.Assertions.assertThat;
  * @author Phillip Webb
  */
 @ExtendWith(OutputCaptureExtension.class)
-@SpringBootTest
+@SpringBootTest(useMainMethod = UseMainMethod.NEVER)
 class SampleLdapApplicationTests {
 
 	@Test