tox: Fix list of py in "debug => use -s" to match main list of py interpreters

I forgot to add py38 and py39 here while adding them in 792cbd6c (tox:
-py36,py37d  +py38d, py38) and 32167853 (tox += CPython3.9). The former
commit also removed py37d from test matrix.

tox.ini

@@ -69,5 +69,5 @@ commands=
 # asan/tsan: tell pytest not to capture output - else it is not possible to see
 # reports from sanitizers because they crash tested process on error.
 # likewise for python debug builds.
-        asan,tsan,py{27,37}d: -s    \
+        asan,tsan,py{27,38,39}d: -s    \
         gpython/ golang/