Test only added and changed yaml files in CI

Makefile

@@ -60,10 +60,9 @@ test-compile-changed: os-autoinst/
 test-yaml-valid:
 	@# Get list of changed yaml files. We only want to lint changed files for
 	@# now because yamllint complains about a lot of existing files
-	$(eval YAMLS=$(shell sh -c "git ls-files schedule/ test_data/ | grep '/.*\.y.\?ml$$'"))
-	export PERL5LIB=${PERL5LIB_} ; tools/test_yaml_valid $(YAMLS);\
 	$(eval CHANGED_YAMLS=$(shell sh -c "git --no-pager diff --diff-filter=dr --name-only FETCH_HEAD `git merge-base FETCH_HEAD origin/master` | grep '\(schedule\|test_data\)/.*\.y.\?ml$$'"))
 	if test -n "$(CHANGED_YAMLS)"; then \
+      export PERL5LIB=${PERL5LIB_} ; tools/test_yaml_valid $(CHANGED_YAMLS);\
 	  which yamllint >/dev/null 2>&1 || echo "Command 'yamllint' not found, can not execute YAML syntax checks";\
 	  yamllint -c .yamllint $(CHANGED_YAMLS);\
 	else \