Bump junit from 4.12 to 4.13.1 in /agent (#1307)

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](https://github.com/junit-team/junit4/compare/r4.12...r4.13.1)

---
updated-dependencies:
- dependency-name: junit:junit
  dependency-type: direct:development
...

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agent/pom.xml

@@ -20,7 +20,7 @@
     <properties>
         <shade.package>cn.hippo4j.agent.dependencies</shade.package>
         <compiler.version>1.8</compiler.version>
-        <junit.version>4.12</junit.version>
+        <junit.version>4.13.1</junit.version>
         <powermock.version>2.0.7</powermock.version>
         <mockito-core.version>3.5.13</mockito-core.version>
         <lombok.version>1.18.20</lombok.version>