d/rules: export junit-xml style test report when building on jenkins

Signed-off-by: Mattia Rizzolo <mattia@debian.org>

debian/rules

@@ -25,6 +25,10 @@ export PYBUILD_TEST_ARGS = -vv -r sxX -l --cov=diffoscope --cov-report=term-miss
 export PYBUILD_AFTER_TEST = debian/tests/basic-command-line
 export PYBUILD_AFTER_INSTALL = rm -rvf '{destdir}/{install_dir}/htmlcov' '{destdir}/{install_dir}/.coverage'
 
+ifneq ($(JENKINS_EXPORTS_DIR),)
+export PYBUILD_TEST_ARGS += --junit-xml=$(JENKINS_EXPORTS_DIR)/test-results/tests.xml
+endif
+
 %:
 	dh $@ --with python3 --with bash-completion --buildsystem=pybuild