tests: Discover pytest tests only in tests/

We only run the tests in `tests/` as part of our test suite, and so if
any external contributor wants to run our test suite, this is what
`pytest` should discover by default.

Signed-off-by: Matt Wozniski <mwozniski@bloomberg.net>

Author: godlygeek

pyproject.toml

@@ -108,3 +108,4 @@ show_missing = true
 # pytest retains all temp files from the last 3 test suite runs by default.
 # Keep only ones for failed tests to avoid filling up a disk.
 tmp_path_retention_policy = "failed"
+testpaths = ["tests"]