Bump junit from 4.12 to 4.13.1 in /core

Bumps [junit](https://github.com/junit-team/junit4) from 4.12 to 4.13.1.
- [Release notes](https://github.com/junit-team/junit4/releases)
- [Changelog](https://github.com/junit-team/junit4/blob/main/doc/ReleaseNotes4.12.md)
- [Commits](junit-team/junit4@r4.12...r4.13.1)

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

core/pom.xml

@@ -18,7 +18,7 @@
         <java.target>1.8</java.target>
 
         <jgit.version>5.9.0.202009080501-r</jgit.version>
-        <junit.version>4.12</junit.version>
+        <junit.version>4.13.1</junit.version>
     </properties>
 
     <dependencies>