[SPARK-40654][PROTOBUF][FOLLOW-UP] Clean up SBT build in Proto component
[SPARK-40654][PROTOBUF][FOLLOW-UP] Clean up SBT build in Proto component

### What changes were proposed in this pull request?

This PR cleans up the syntax, and properly copy protobuf assembly jar (currently it copies connect assembly jar by mistake).

### Why are the changes needed?

For consistent code style, and correct SBT build.

### Does this PR introduce _any_ user-facing change?
No, this isn't released yet.

### How was this patch tested?

CI in this PR should test it out.

Closes #38240 from HyukjinKwon/SPARK-40654.

Authored-by: Hyukjin Kwon <2680965ad5aae29275c8fb10150cb10f5554e78b@apache.org>
Signed-off-by: Hyukjin Kwon <2680965ad5aae29275c8fb10150cb10f5554e78b@apache.org>

ueshin/apache-spark,hvanhovell/spark,ueshin/apache-spark,shaneknapp/spark,mahak/spark,vinodkc/spark,wangyum/spark,wangyum/spark,mahak/spark,vinodkc/spark,HyukjinKwon/spark,vinodkc/spark,dongjoon-hyun/spark,mahak/spark,wangyum/spark,shaneknapp/spark,zzcclp/spark,zzcclp/spark,HyukjinKwon/spark,dongjoon-hyun/spark,dongjoon-hyun/spark,HyukjinKwon/spark,vinodkc/spark,srowen/spark,HyukjinKwon/spark,dongjoon-hyun/spark,dongjoon-hyun/spark,vinodkc/spark,dongjoon-hyun/spark,wangyum/spark,shaneknapp/spark,wangyum/spark,shaneknapp/spark,HyukjinKwon/spark,hvanhovell/spark,srowen/spark,ueshin/apache-spark,hvanhovell/spark,zzcclp/spark,hvanhovell/spark,apache/spark,zzcclp/spark,srowen/spark,apache/spark,mahak/spark,apache/spark,apache/spark,hvanhovell/spark,apache/spark,ueshin/apache-spark,mahak/spark,ueshin/apache-spark,ueshin/apache-spark,hvanhovell/spark,HyukjinKwon/spark,zzcclp/spark,apache/spark,hvanhovell/spark,srowen/spark,srowen/spark,vinodkc/spark,shaneknapp/spark,mahak/spark,wangyum/spark,mahak/spark,HyukjinKwon/spark,shaneknapp/spark,zzcclp/spark,ueshin/apache-spark,shaneknapp/spark,vinodkc/spark,wangyum/spark,srowen/spark,srowen/spark,zzcclp/spark,dongjoon-hyun/spark,apache/spark