fix: use importlib.import_module instead of __import__

`import_module` is newer, and provides a couple of advantages over a bare `__import__`:
> The import_module() function acts as a simplifying wrapper around importlib.__import__(). This means all semantics of the function are derived from importlib.__import__(). The most important difference between these two functions is that import_module() returns the specified package or module (e.g. pkg.mod), while __import__() returns the top-level package or module (e.g. pkg).

It's unclear if this will actually fix any problems in the real world, but there's no recent to use `__import__` at this point AFAICT.

Author: bhearsum

src/taskgraph/util/python_path.py

@@ -2,6 +2,7 @@
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
+import importlib
 import inspect
 import os
 
@@ -19,9 +20,7 @@ def find_object(modulepath, objectpath):
         raise ValueError(f'python path {path!r} does not have the form "module:object"')
 
     modulepath, objectpath = path.split(":")
-    obj = __import__(modulepath)
-    for a in modulepath.split(".")[1:]:
-        obj = getattr(obj, a)
+    obj = importlib.import_module(modulepath)
     for a in objectpath.split("."):
         obj = getattr(obj, a)
     return obj