Notebook magic used old terminology "input"

replace by 'source'.

Fixes  #8028

IPython/core/magics/basic.py

@@ -603,7 +603,7 b' Defaulting color scheme to \'NoColor\'"""'
             hist = list(self.shell.history_manager.get_range())
             if(len(hist)<=1):
                 raise ValueError('History is empty, cannot export')
-            for session, execution_count, input in hist[:-1]:
+            for session, execution_count, source in hist[:-1]:
                 cells.append(v4.new_code_cell(
                     execution_count=execution_count,
                     source=source

IPython/core/tests/test_magic.py

@@ -625,7 +625,7 b' class NotebookExportMagicTests(TestCase):'
     def test_notebook_export_json(self):
         _ip = get_ipython()
         _ip.history_manager.reset()   # Clear any existing history.
-        cmds = [u"a=1", u"def b():\n  return a**2", u"print(a, b())"]
+        cmds = [u"a=1", u"def b():\n  return a**2", u"print('noël, été', b())"]
         for i, cmd in enumerate(cmds, start=1):
             _ip.history_manager.store_inputs(i, cmd)
         with TemporaryDirectory() as td: