tests: Add another testcase for relative imports.

tests/import/import_pkg6.py

@@ -0,0 +1,2 @@
+# This tests relative imports as used in pkg6
+import pkg6

tests/import/pkg6/__init__.py

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+from .x import *
+print('init')

tests/import/pkg6/x/__init__.py

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+from .y import *
+print('x')

tests/import/pkg6/x/y.py

@@ -0,0 +1 @@
+print('y')