load-task: ensure .bashrc is readable by the worker user

For some reason (presumably due to using podman instead of docker), I'm
getting a root-owned 0600 .bashrc, meaning I can't actually run
exec-task.

Author: jcristau

src/taskgraph/docker.py

@@ -346,6 +346,7 @@ def load_task(task_id, remove=True, user=None):
 
         if task_command:
             initfile = tempfile.NamedTemporaryFile("w+", delete=False)
+            os.fchmod(initfile.fileno(), 0o644)
             initfile.write(
                 dedent(
                     f"""