Fix error on tab completions (ipython#15076)

### Fixes ipython#15075 

### Description
Added a logic to check whether the node we have is `ast.Expr` before
trying to access its `value`.

Author: krassowski

IPython/core/completer.py

@@ -1352,6 +1352,8 @@ def _trim_expr(self, code: str) -> str:
             assert res is not None
             if len(res.body) != 1:
                 continue
+            if not isinstance(res.body[0], ast.Expr):
+                continue
             expr = res.body[0].value
             if isinstance(expr, ast.Tuple) and not code[-1] == ")":
                 # we skip implicit tuple, like when trimming `fun(a,b`<completion>

tests/test_completer.py

@@ -2688,6 +2688,7 @@ def test_misc_no_jedi_completions(setup, code, expected, not_expected):
         ("x = {1, y", "y"),
         ("x = [1, y", "y"),
         ("x = fun(1, y", "y"),
+        (" assert a", "a"),
     ],
 )
 def test_trim_expr(code, expected):