[traits.build testing] Increase efficiency and accessibility of dataset_test

[yangsophieee]

Speed of running dataset_test is very slow on the whole austraits directory. The current GitHub workflow has dataset_test which builds the datasets, but the workflow also builds the database again later.

Also according to @ehwenk it's hard to find the failed test in dataset_test when run via GitHub actions because there are thousands to scroll through. Need to investigate the testthat reporter.