ci: move some variables closer to their usage

These were defined globaly because we had trouble making them inherited. This
is now fixed, so we can get them were they belong.

contrib/heptapod-ci.yml

@@ -32,8 +32,6 image: registry.heptapod.net/mercurial/c
 variables:
     PYTHON: python
     HG_CI_IMAGE_TAG: "v2.1"
-    TEST_HGTESTS_ALLOW_NETIO: "0"
-    SHOW_VERSION_OF: "$PYTHON"
 
 .all:
   # help changing all job at once when debugging
@@ -81,6 +79,9 build-c-wheel:
 .runtests:
     extends: .all
     stage: tests
+    variables:
+      SHOW_VERSION_OF: "$PYTHON"
+      TEST_HGTESTS_ALLOW_NETIO: "0"
     # The runner made a clone as root.
     # We make a new clone owned by user used to run the step.
     before_script: