Delay import from matplotlib_inline.backend_inline (#14330) Possible fix for #14329. With this change, the reproducers from the issue become: ```python $ ipython <snip> In [1]: import matplotlib.pyplot as plt; plt.set_loglevel("debug") In [2]: %matplotlib tk DEBUG:matplotlib.pyplot:Loaded backend TkAgg version 8.6. ``` It is still possible to call `matplotlib.pyplot.switch_backend` twice but only if you request `%matplotlib inline`, and the `switch_backend` is called with same correct backend twice. This isn't ideal but it doesn't cause any problems apart from being a little slower than necessary.