### What changes were proposed in this pull request?
This PR proposes to explicitly cache and hash the files/directories under 'build' for SBT and Zinc at GitHub Actions. Otherwise, it can end up with overwriting `build` directory. See also https://github.com/apache/spark/pull/29286#issuecomment-679368436
Previously, other files like `build/mvn` and `build/sbt` are also cached and overwritten. So, when you have some changes there, they are ignored.
### Why are the changes needed?
To make GitHub Actions build stable.
### Does this PR introduce _any_ user-facing change?
No, dev-only.
### How was this patch tested?
The builds in this PR test it out.
Closes#29536 from HyukjinKwon/SPARK-32695.
Authored-by: HyukjinKwon <gurwls223@apache.org>
Signed-off-by: HyukjinKwon <gurwls223@apache.org>
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