fix(ggshield-not-ci): correct logic and print when skipping (#4)

hooks/ggshield-not-ci.sh

@@ -1,6 +1,8 @@
 #!/usr/bin/env bash
 set -eo pipefail
 
-if [[ ! -z "${CI}"} ]]; then
+if [[ -z "${CI}" ]]; then
   ggshield secret scan pre-commit
+else
+  echo "In a CI environment, so skipping GitGuardian ggshield"
 fi