gitlab-ci: skip python black check during make check for builds

We now install black by default via REQUIRED_PACKAGES script.
Thus, also when we build on Fedora 30, `make check` would run
python black. However, the formatting depends on the version
of python black, and the one in Fedora 30 is not right.

Skip all black tests during `make check`. We have a deicated
gitlab-ci test that runs black already (with the desired version
of black).

.gitlab-ci/build.sh

@@ -19,6 +19,12 @@ meson --version
 ! which dpkg || dpkg -l
 ! which yum  || yum list installed
 
+# The formatting depends on the version of python black.
+# We have a dedicated test that checks our formatting, which
+# uses the right version. We should disable the check during
+# `make check`.
+export NMTST_SKIP_PYTHON_BLACK=1
+
 do_clean; BUILD_TYPE=autotools CC=gcc   WITH_DOCS=1 WITH_VALGRIND=1 contrib/scripts/nm-ci-run.sh
 rm -rf /tmp/nm-docs-html;
 mv build/INST/share/gtk-doc/html /tmp/nm-docs-html