chore: speedup pytest

Specifying the particular directory with tests
significantly speeds up their collection and execution.

Before:

```console
$ time pytest -k nothing
12 deselected in 1.36s
```

After:

```
12 deselected in 0.04s
```

pytest.ini

 [pytest]
+testpaths =
+    test/int
 addopts =
     -v
-    --ignore tarantool
-    --ignore tarantool-sys
-    --ignore tarantool-patches