Fix indentation problem with _asyncify

If the input to `_asyncify` contains newlines, the strategy of indenting
and then truncating the first 8 characters won't work, since the first,
empty line doesn't get indented. Instead I've changed the format string
to accept the normal output of textwrap.indent() without modification.

IPython/core/async_helpers.py

@@ -69,14 +69,14 b' def _asyncify(code: str) -> str:'
     And setup a bit of context to run it later.
     """
     res = dedent(
-        """
-        async def __wrapper__():
-            try:
-                {usercode}
-            finally:
-                locals()
     """
-    ).format(usercode=indent(code, " " * 8)[8:])
+    async def __wrapper__():
+        try:
+    {usercode}
+        finally:
+            locals()
+    """
+    ).format(usercode=indent(code, " " * 8))
     return res