pin the version using SHA

Signed-off-by: Samia Wear <samia.wear1@nhs.net>

Author: samia-nhse

tools/gitleaks.md

@@ -61,7 +61,7 @@ Example GitHub Actions step:
   run:  docker run --rm --platform linux/amd64 \
             -v "$(pwd):/repo" \
             -w /repo \
-            ghcr.io/gitleaks/gitleaks:v8.30.1 \
+            ghcr.io/gitleaks/gitleaks@sha256:c00b6bd0aeb3071cbcb79009cb16a60dd9e0a7c60e2be9ab65d25e6bc8abbb7f \
             git --source /repo --redact --verbose --log-opts="--all"
 ```