tests/import: Improve builtinimport.c test coverage.

tests/import/import_pkg7.py

-# This tests ... relative imports as used in pkg7
+# This tests ... relative imports as used in pkg7 and imports beyond package root
 import pkg7.subpkg1.subpkg2.mod3

tests/import/import_pkg8.py

+# import with no __init__.py files
+import pkg8.mod

tests/import/pkg7/subpkg1/subpkg2/mod3.py

@@ -2,3 +2,10 @@ from ... import mod1
 from ...mod2 import bar
 print(mod1.foo)
 print(bar)
+
+# when attempting relative import beyond top-level package uPy raises ImportError
+# whereas CPython raises a ValueError
+try:
+    from .... import mod1
+except (ImportError, ValueError):
+    print('Error')

tests/import/pkg8/mod.py

+print('foo')