dslx_test allows for multiple deps but only runs tests in one of them

[dank-openai]

Description

The dslx_test rule allows for multiple items in the deps field. Then it runs the tests in just one of them. This is bad because it's not running the tests in the other deps item(s), which is very confusing.

Expected behavior

I expect one of the following, preferably the first:

• Only allow one item in deps. In fact, make the expected type just a string, not a list of strings.
• Run tests found in all items of deps.