pytype: update check-pytype.sh to select target automatically

We have python3.11 on CI, so we can run pytype targeting that version. On the
other hand, we don't have python3.7 on CI anymore, so we can't run pytype for
3.7 anymore (interpreter not found). I think it's fine to make pytype select
the appropriate target depending on the version of the interpreter it's running
under.

contrib/check-pytype.sh

@@ -71,7 +71,7 b' cd `hg root`'
 
 # TODO: include hgext and hgext3rd
 
-pytype -V 3.7 --keep-going --jobs auto \
+pytype --keep-going --jobs auto \
     doc/check-seclevel.py hgdemandimport hgext mercurial \
     -x hgext/absorb.py \
     -x hgext/bugzilla.py \