bpo-43797: Improve syntax error for invalid comparisons (#25317)

* bpo-43797: Improve syntax error for invalid comparisons

* Update Lib/test/test_fstring.py

Co-authored-by: Guido van Rossum <gvanrossum@gmail.com>

* Apply review comments

* can't -> cannot

Co-authored-by: Guido van Rossum <gvanrossum@gmail.com>
diff --git a/Lib/test/test_exceptions.py b/Lib/test/test_exceptions.py
index 1e6f525..9dc3a81 100644
--- a/Lib/test/test_exceptions.py
+++ b/Lib/test/test_exceptions.py
@@ -260,7 +260,7 @@ def baz():
         check('[*x for x in xs]', 1, 2)
         check('foo(x for x in range(10), 100)', 1, 5)
         check('for 1 in []: pass', 1, 5)
-        check('(yield i) = 2', 1, 2)
+        check('(yield i) = 2', 1, 11)
         check('def f(*):\n  pass', 1, 8)
 
     @cpython_only