run-test.py: greatly increase the priority of 'check-code' tests

As check-code is actually quite long to run for its file size, this prevent them
to be scheduled too late during the test run.

This reduces my typical test run from 107 seconds to 90 seconds

tests/run-tests.py

@@ -1664,7 +1664,7 b' class TestRunner(object):'
             # keywords for slow tests
             slow = {b'svn': 10,
                     b'gendoc': 10,
-                    b'check-code-hg': 10,
+                    b'check-code-hg': 100,
                    }
             def sortkey(f):
                 # run largest tests first, as they tend to take the longest