user/erlang: test suite failures are masked; package builds "successfully"

We normally expect test failures to cause the package to fail to build.

At least as of 24.0.1 (likely earlier), and at least through 27.0.1, test suite failures do not cause the package to fail to build:

...
 peer:start_it failed on line 929
Reason: timeout
...
>>> erlang: Build complete at Thu, 25 Jul 2024 23:27:48 +0000 elapsed time 0h 9m 2s
...

marked this issue as related to #1227

Note that during my debugging of Elixir, I noticed a few failures that have also been plaguing the Docker Elixir team (it was related to timezones, something I didn't see locally).

The official docs explicitly call out you need to check an HTML page to determine success or failure, so I'm not sure what we're meant to do unless we grep the HTML…