Upgrade JUnit BoM to 5.7.1

We are not using Jupiter yet, but this is nice to have for the future.
Thanks to @larsgrefer for his initiative to prepare AspectJ for
JUnit Jupiter and for his other PR which also contains the same change
in the parent POM. :-)

Signed-off-by: Alexander Kriegisch <Alexander@Kriegisch.name>

pom.xml

@@ -324,7 +324,7 @@
 			<dependency>
 				<groupId>org.junit</groupId>
 				<artifactId>junit-bom</artifactId>
-				<version>5.6.2</version>
+				<version>5.7.1</version>
 				<type>pom</type>
 				<scope>import</scope>
 			</dependency>