tests/run-tests.py: Set __main__ module to __injected_test.

When using unittest (for example) with injected mpy files, not only does
the name of the main test module need to be `__main__`, but also the
`__main__` module should correspond to this injected module.  Otherwise the
unittest test won't be detected.

Signed-off-by: Damien George <damien@micropython.org>

tests/run-tests.py

@@ -65,7 +65,9 @@ injected_import_hook_code = """\
 import sys, os, io, vfs
 class __File(io.IOBase):
   def __init__(self):
-    sys.modules['__injected_test'].__name__ = '__main__'
+    module = sys.modules['__injected_test']
+    module.__name__ = '__main__'
+    sys.modules['__main__'] = module
     self.off = 0
   def ioctl(self, request, arg):
     if request == 4: # MP_STREAM_CLOSE