fix: Change boolean variable behaviour

Signed-off-by: Cédric OLIVIER <cedric3.olivier@orange.com>

templates/gitlab-ci-gitleaks.yml

@@ -187,7 +187,7 @@ stages:
     fi
   }
 
-  if [[ -z "$TEMPLATE_CHECK_UPDATE_DISABLED" ]]; then check_for_update gitleaks "1.2.0"; fi
+  if [[ "$TEMPLATE_CHECK_UPDATE_DISABLED" != "true" ]]; then check_for_update gitleaks "1.2.0"; fi
   unscope_variables
 
   # ENDSCRIPT