Update ruff version in checkformat script to use test image

Author: ahosgood

tasks/checkformat.sh

@@ -1,3 +1,4 @@
 #!/bin/bash
 
-docker run --rm -v "$(pwd)":/app/ ghcr.io/nationalarchives/tna-python-dev:preview checkformat
+# TODO: Change ruff version back to preview once the Docker image has been released
+docker run --rm -v "$(pwd)":/app/ ghcr.io/nationalarchives/tna-python-dev:ruff checkformat