Define surefire test provider to use

The `spring-boot-test` module has a dependency to TestNG to validate
some part of the test infrastructure but no tests are actually written
using TestNG. The presence of TestNG is a trigger for the maven surefire
plugin and it attempts to run tests using it.

This commit defines the explicit provider to use (JUnit 4)

Closes spring-projectsgh-16735

spring-boot-project/spring-boot-test/pom.xml

@@ -206,6 +206,17 @@
 					</execution>
 				</executions>
 			</plugin>
+			<plugin>
+				<groupId>org.apache.maven.plugins</groupId>
+				<artifactId>maven-surefire-plugin</artifactId>
+				<dependencies>
+					<dependency>
+						<groupId>org.apache.maven.surefire</groupId>
+						<artifactId>surefire-junit47</artifactId>
+						<version>${maven-surefire-plugin.version}</version>
+					</dependency>
+				</dependencies>
+			</plugin>
 			<plugin>
 				<groupId>org.jetbrains.kotlin</groupId>
 				<artifactId>kotlin-maven-plugin</artifactId>