[KYUUBI #4347] Bump maven download plugin from 1.6.6 to 1.6.8

### _Why are the changes needed?_

- 1.6.8 release note: https://github.com/maven-download-plugin/maven-download-plugin/releases/tag/1.6.8

### _How was this patch tested?_
- [ ] Add some test cases that check the changes thoroughly including negative and positive cases if possible

- [ ] Add screenshots for manual tests if appropriate

- [ ] [Run test](https://kyuubi.readthedocs.io/en/master/develop_tools/testing.html#running-tests) locally before make a pull request

Closes #4347 from bowenliang123/maven-download-plugin-1.6.8.

Closes #4347

947767d1 [liangbowen] bump maven download plugin version from 1.6.6 to 1.6.8

Authored-by: liangbowen <liangbowen@gf.com.cn>
Signed-off-by: liangbowen <liangbowen@gf.com.cn>

pom.xml

@@ -212,7 +212,7 @@
         <jars.target.dir>${project.build.directory}/scala-${scala.binary.version}/jars</jars.target.dir>
 
         <maven.plugin.build.helper.version>3.3.0</maven.plugin.build.helper.version>
-        <maven.plugin.download.version>1.6.6</maven.plugin.download.version>
+        <maven.plugin.download.version>1.6.8</maven.plugin.download.version>
         <maven.plugin.enforcer.mojo.rules.version>1.6.1</maven.plugin.enforcer.mojo.rules.version>
         <maven.plugin.scala.version>4.8.0</maven.plugin.scala.version>
         <maven.plugin.surefire.version>3.0.0-M8</maven.plugin.surefire.version>