Stop deferring JPA bootstrap mode by default

This commit changes the default value of bootstrap-mode to "default"
rather than "deferred" so that the JPA infrastructure starts in the
main thread rather than asynchronously.

Closes gh-24249

spring-boot-project/spring-boot-test-autoconfigure/src/test/java/org/springframework/boot/test/autoconfigure/orm/jpa/DataJpaTestIntegrationTests.java

@@ -109,9 +109,9 @@ class DataJpaTestIntegrationTests {
 	}
 
 	@Test
-	void bootstrapModeIsLazyByDefault() {
+	void bootstrapModeIsDefaultByDefault() {
 		assertThat(this.applicationContext.getEnvironment().getProperty("spring.data.jpa.repositories.bootstrap-mode"))
-				.isEqualTo(BootstrapMode.LAZY.name());
+				.isEqualTo(BootstrapMode.DEFAULT.name());
 	}
 
 }