[fix][core] regex parsing for si ff

us: PRODX-5418
Change-Id: I604d43b15f0ba507822f6421d387852862b8b66c
diff --git a/src/com/mirantis/mk/KaasUtils.groovy b/src/com/mirantis/mk/KaasUtils.groovy
index a9c7e27..b6dc191 100644
--- a/src/com/mirantis/mk/KaasUtils.groovy
+++ b/src/com/mirantis/mk/KaasUtils.groovy
@@ -128,7 +128,7 @@
             "kaas-si-test-${siTestsRefspec.split('/')[-2]}:${siTestsRefspec.split('/')[-1]}"
     }
     if (siFeatureFlagsMatches.size() > 0) {
-        siTestsFeatureFlags = siFeatureFlagsMatches.size[0][0].split('si-feature-flags')[1].replaceAll('[\\[\\]]', '').trim()
+        siTestsFeatureFlags = siFeatureFlagsMatches[0][0].split('si-feature-flags')[1].replaceAll('[\\[\\]]', '').trim()
     }
     if (siPipelinesMatches.size() > 0) {
         siPipelinesRefspec = siPipelinesMatches[0][0].split('si-pipelines-ref')[1].replaceAll('[\\[\\]]', '').trim()