### What changes were proposed in this pull request?
Two different versions are used for the same artifacts, `exec-maven-plugin` and `scalatest-maven-plugin`. This PR aims to use the same versions for `exec-maven-plugin` and `scalatest-maven-plugin`. In addition, this PR removes `scala-maven-plugin.version` from `K8s` integration suite because it's unused.
### Why are the changes needed?
This will prevent the mistake which upgrades only one place and forgets the others.
### Does this PR introduce _any_ user-facing change?
No.
### How was this patch tested?
Pass the Jenkins K8S IT.
Closes#29248 from dongjoon-hyun/SPARK-32448.
Authored-by: Dongjoon Hyun <dongjoon@apache.org>
Signed-off-by: Dongjoon Hyun <dongjoon@apache.org>
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