Modernise importlib usage

`find_module` is deprecated in all supported version of Python and
is slated for removal in the upcoming 3.12. Happily it seems we
can move to the related `find_spec` and just hoist the loader from
the spec which that returns. (This is mostly what current `find_module`
implementations do anyway).

jedi/inference/compiled/subprocess/__main__.py

@@ -21,11 +21,11 @@ class _ExactImporter(MetaPathFinder):
     def __init__(self, path_dct):
         self._path_dct = path_dct
 
-    def find_module(self, fullname, path=None):
+    def find_spec(self, fullname, path=None, target=None):
         if path is None and fullname in self._path_dct:
             p = self._path_dct[fullname]
-            loader = PathFinder.find_module(fullname, path=[p])
-            return loader
+            spec = PathFinder.find_spec(fullname, path=[p], target=target)
+            return spec
         return None