bug#62092: 30.0.50; "case" does not work as dedenter in Python

[Mattias Engdegård]

The test python-info-dedenter-opening-block-positions-7 added as part of this 
bug in 8f42db010d ends with

+   (equal (list (python-tests-look-at "case 2:" -1)
+                (python-tests-look-at "case 1:" -1 t))
+            (python-info-dedenter-opening-block-positions))))

which, as you can see, isn't actually a check; the `equal` result is thrown 
away.
(Emacs master was just changed to detect this, so there is a byte-compiler 
warning.)

Unfortunately, wrapping the call in `should` fails, so there is more to it.
Would you please take a look?