Convert environment used by SpringBootTestContextLoader

This commit aligns `SpringBootTest`s to also use `ApplicationEnvironment`
instead of `StandardEnvironment`. This prevents the side-effect of active
profiles from `@ActiveProfiles` from being added to the environment when
doGetActiveProfiles is called. In this case, calling `addActiveProfiles()`
in the environment post processor would result in `@ActiveProfiles` being
added to the environment first, resulting in the wrong order.

The additional call to `setActiveProfiles()` is also not necessary when using
ApplicationEnvironment because that call was put in place to prevent the side-effect
which `ApplicationEnvironment` does not have.

Fixes gh-28530

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/SpringApplication.java

@@ -377,13 +377,24 @@ public class SpringApplication {
 				"Environment prefix cannot be set via properties.");
 		bindToSpringApplication(environment);
 		if (!this.isCustomEnvironment) {
-			environment = new EnvironmentConverter(getClassLoader()).convertEnvironmentIfNecessary(environment,
-					deduceEnvironmentClass());
+			environment = convertEnvironment(environment);
 		}
 		ConfigurationPropertySources.attach(environment);
 		return environment;
 	}
 
+	/**
+	 * Convert the given {@link ConfigurableEnvironment environment} to an application
+	 * environment that doesn't attempt to resolve profile properties directly.
+	 * @param environment the environment to convert
+	 * @return the converted environment
+	 * @since 2.5.7
+	 */
+	public StandardEnvironment convertEnvironment(ConfigurableEnvironment environment) {
+		return new EnvironmentConverter(getClassLoader()).convertEnvironmentIfNecessary(environment,
+				deduceEnvironmentClass());
+	}
+
 	private Class<? extends StandardEnvironment> deduceEnvironmentClass() {
 		switch (this.webApplicationType) {
 		case SERVLET: